I've been doing quite a bit more research on this subject of Christos v. Chrestos. Coincidentally, someone sent me an interesting document that included a link to this PDF:
Chrestians before Christians? An Old Inscription Revisited
by Erik Zara, ThD
In the 18th century the Italian historian Lodovico Antonio Muratori collected many ancient inscriptions in the work Novus Thesaurus Veterum Inscriptionum. Amongst them, one marble inscription, originally from Rome,1 has puzzled some scholars. The inscription, an epitaph, given the Corpus Inscriptionum Latinarum identity number CIL VI 24944,2 reads:
M. T. DRVSI . PATERES
PRIMICINIO3. QVI VIXIT
ANN. XXXXII. DIES VII
FAVSTVS. ANTONIAE. DRVSI. IVS EMIT. IVCVNDI. CHRESTIANI. OLL4
According to Dr. Heinrich Chantraine, the stone cutter severely disfigured the text and it is “nicht sicher zu heilen.”5 “D.M.” is an abbreviation of “Diis Manibus”, “to the gods of the underworld”, and has been said to indicate that the grave was a pagan’s grave.6 The text, being difficult to interpret as it is missing “essential” words, could be interpreted as saying that M. (and) T.7, the father/fathers8 of Drusus, dedicated the tomb to his/their first born9 son, who lived for 42 years and seven days, and Faustus, the son/slave/freedman of Antonia, the daughter/wife10 of Drusus, bought (emit) the right for the urn (with cremation ashes) to be put in a certain columbarium or other burial place (jus oll.),11 from Jucundus, the Chrestian.
“Antonia” has often been interpreted as referring to Antonia Minor (36 BCE - 37 CE),12 the daughter of Mark Anthony the triumvir, and mother of the emperor Claudius. She was married to General Nero Claudius Drusus, from (18 or) 16 BCE until he died in 9 BCE.13 Faustus has been regarded as a freedman14, servant15 or slave16 of Antonia. It is not possible, based only on the information given, to conclude with absolute certainty that the Antonia and Drusus in the inscription actually are the famous Antonia and Drusus mentioned above.17 “Jucundus Chrestianus” has by some been interpreted as referring to a Christian person, who no longer needed the right to put his urn in a certain place (because Christians did not cremate their dead) and thus sold this right to a pagan.18 Jucundus19 (meaning pleasant, delightful or agreeable20), was by Dr. Johann Sepp thought of as one of the earliest Christian believers in Rome.21 Others believe that Chrestianus (perhaps deriving from the Greek word chrêstos, meaning good, useful, and service-able22, which was a common name23) was the person’s proper name.24 If Chrestianus is not a servant’s name, it could be referring to a person belonging to the new religion (i.e. Christianity), Dr. Marta Sordi concludes.25. Dr. Joseph B. Lightfoot has stated, regarding Chrestianus, that the name is improbable and that it is not known to have existed, and the name is rarely used, and seems unused in the 1st century CE.26
Regarding the dating of the inscription, it has been said that it cannot have been made later than 37 CE, the year Antonia Minor died.27 Dr. Martin Karrer, who seems to agree about this dating, calls the inscription the earliest documentation of the word Chrestianus,28 a word non-Christians used, referring to Christians, in the days of Tertullian (very late second century).29...
...On the whole, no indisputably Christian inscriptions seem to exist, which can be dated to earlier than about 200 CE
, and most Christian epigraphs are from the 3rd century or later.38
Unfortunately, the author misses the opportunity to emphasize that the earliest extant Bible manuscript has in three places not the word "Christian(s)" but "Chrestian(s)." Instead he says so in a footnote:
In the earliest extant complete bible, Codex Sinaiticus (4th cent), the Greek words are even spelled [chrestianou], [chrestianon] and [chrestianos], i.e. Chrestian/Chrestians....
Then Zara concludes:
Since indeed no usage of the apparently very uncommon proper name or cognomen Chrestianos or Chrestianus, in Rome, during the life time of Antonia Minor, or the rest of the first century, can be confirmed, and since no known group seems to have been called Christiani or Chrestiani before 37 CE (and the Christians did not call themselves Christians until later, in their own documents), I conclude that the inscription, if correctly interpreted and dated, probably refers to something else.50 Perhaps Jucundus was a part of a group called the “Chrestians”, but as no external evidence in support of such a notion exists, I will leave the subject without further conclusions about the meaning of the word Chrestiani here.
While this conclusion is minimalist, scientifically based on the extant evidence, it should be noted that before this inscription was found, this term "Chrestian" was supposedly unknown in the first century. Yet, here is the evidence that it was not unknown - there may have been more evidence of this term, if it was ever written down, since it might be part of the mysteries, that was destroyed long ago. Moreover, it needs to be reiterated that "Chrestian" is the precise term used in the earliest New Testament manuscript, and one could certainly posit it is part of the same tradition. It is puzzling that Zara chose to ignore the Sinaiticus Bible by including it as an aside and then not factoring it into his conclusion, but he is
Furthermore, we must include in this analysis the fact the Marcionites followed "Jesus the Good," i.e., Jesus Chrest, and that the earliest known extant church is a Marcionite one in Egypt with the name "Jesus the Chrest" over the doorway. In addition, in the OT we find passages in which the Lord is called "the Good" or "Chrestos"; hence, it is already in pre-Christian times an epithet for God. What appears to be happening is one faction with its favored epithet "Jesus the Chrest" and another, the more Jewish one, favoring the epithet "Jesus the Christ." The "Chrest" appears to be the earliest tradition, one that obviously extended into the fourth century, when the Codex Sinaiticus was written. At what time the words were altered to "Christian(s), I do not know. I would hope someone has done a study of that issue, but so many are timid and afraid of stepping on toes just by acknowledging this alteration occurred in the first place.
Here's another one from Erik Zara, this time about the word "Chrestianos" in Tacitus.The Chrestianos Issue in Tacitus Reinvestigated
This one cites another apparent error on the part of Richard Carrier:
Some (like Richard Carrier, Ph.D.) have recently (autumn 2008) argued that earlier scholars like Harald Fuchs have erred, when they asserted that the word Christianos (Christians) originally was spelled Chrestianos (Chrestians), i.e. with an “e” instead of the now present “i”. This view seems to be generally accepted, and is repeated in textbooks.6 I will not detail all the arguments regarding the subject, but only mention a few. An argument in favor of the Chrestianos-position has been that the “ri” in the word is written in a different way than the “ri”-combination usually is, in the manuscript. Against this, it has been claimed that the scribe only “goofed” by writing “i” in a different style compared to what he normally did after the letter “r”. Georg Andresen found in 1902 that there is an (unusual) gap between the “i” and the “s” in the word, and that this has been over bridged (in fact under bridged) by a hyphen, which led him to believe that the “i” was corrected from an original “e”. According to Andresen, the “bulb” of the “e” filled out the now empty space.7 Others, like Carrier, have claimed that the space isn’t that unusual, and that the letter thus not of necessity was altered.
Harald Fuchs asked the then-director of the Biblioteca Medicea Laurenziana, Dr. Teresa Lodi, to examine the document. She wrote to him: «The "e", written originally, of which there are still signs left at the erased area [Italian: rasura], was changed into "i" taking out the upper circle and the horizontal line, while the remaining part was corrected, in my opinion, with the same ink and the same hand, towards an "i". Another hand added the dot above the "i" and the hyphen between "i" and "s"»8 I have not found any examination of the original manuscript refuting the conclusions made by Dr. Lodi, but still her study is at least 58 years old, and the technique has since become better....
When I got an ultraviolet photograph of the manuscript, I could see that the change of the “e” into an “i”, was clearly visible. The traces of the erased “e” can be seen...
This part is odd, however:
For the sake of clarity, I will add that this particular manuscript of Annales does not contain the name Chrestus. No evidence of any alteration of the word “Christus” can be found in the ultraviolet photograph.
This part refers to the following passage in Tacitus:
Consequently, to get rid of the rumor [that Nero ordered the fire], Nero fastened the guilt and inflicted the most exquisite tortures on a class hated for their abominations, called Christians by the populace. Christus [i.e. Christ], the author of the name....
Why would they be called "Chrestians," if the "author" of the "class" was called "Christus?"