Why did people date divorce documents according to the Greeks?

Question

According to this article on Jewish Encyclopedia, the conventional Jewish system of dating documents in the Middle Ages (a system called "מנין שטרות") was related to the accession of Seleucus I, the first king of the Seleucid dynasty. This Hebrew article on Wikipedia explains how it came to be that Jews associated this dating system with the arrival of Alexander and the cessation of prophecy. From that same article, it appears that this was a common system for the dating of ketubot, gittin, colophons and financial documents until the 9th century, although it persisted for Egyptian Jews until the 16th century, and for Yemenite Jews until the 20th.

[For a beautiful example of a colophon that employs this system, see this image from the Leningrad Codex, completed c.1008. It utilises a number of different dates, but the relevant one is at the end of the third line: והיא שנת אלף ושלש מאות ותשע עשרה שנה למלכות יונים שהיא למנין {שטרות} ולפסיקת הנבואה.]

My question, based on the foregoing, is as follows:

The Mishna, in Gittin 8:5, specifically forbids dating a divorce document in accordance with the Greek empire (לשום מלכות יון), and the gemara (Gittin 80a-b) does not appear to qualify this in any respect. What is more, neither Rashi nor the Tosafot raise any objections to this, despite it having been the custom to do so until only a couple of centuries earlier!

Why was dating divorce documents in accordance with the Seleucid Empire not problematic for Jews? Alternatively, how do I learn this mishna (and the corresponding gemara) in such a way that it is not suggesting that this practice should be forbidden? (Or, thirdly, is the author of the Wikipedia article mistaken, and this system was never used for שטרות גירושין?)

Answer 1

In the Bavli to that Mishna (Gittin 80a), 'Ula explains that the reason there was an enactment made to write the date according to the local government was "משום שלום מלכות" "to maintain peace with the government". Rashi explains that the governments would see we use their dating system and assume that we value their leadership. Accordingly, Rambam rules (Hilchot Geirushin 1:27 (English)):

וכן תיקנו שיהיו מונין בגיטין למלכות אותו הזמן, משום שלום מלכות. כתב למלכות שאינה מלכות אותה המדינה, או לבניין הבית, או לחורבן הבית--אם דרך אנשי אותו מקום למנות בו, הרי זה כשר; ואם אין דרכן למנות בו, הרי זה פסול. וכבר נהגו כל ישראל למנות בגיטין, או ליצירה או למלכות אלכסנדרוס מקרון שהוא מניין שטרות. ואם כתב לשם מלכות אותו זמן במדינה שיש בה רשות אותה מלכות, הרי זה כשר.‏
Similarly, [our Sages] ordained that the year of the ruling kingdom of that time should be mentioned in a get to gain the favor of the ruling authorities.

[The following rules apply if] a person writes a get and dated it according to the years of a kingdom other [than that of his locale] or according to the years beginning from the Temple's construction or destruction. If it is customary for people in that locale to date [their documents] in this manner, it is acceptable. If this is not the local custom, it is unacceptable.

It has already become the universal Jewish custom to date gittin from the time of creation, or from the crowning of Alexander the Great, which is [the accepted means of dating] for legal documents. If one dates [a get] according to the years of a contemporary kingdom, it is acceptable only in the country over which that kingdom rules.

It seems that now that governments don't care how we date the documents, it is acceptable to use a local customary system.