1,707. The Date in a Get
Hilchos Geirushin 1:27
The Sages likewise enacted that the year of the current reign be written in a get in order to remain in the good graces of the authorities. Let’s say that someone wrote a get and dated it according to some other kingdom’s reign, or based upon the years from the Temple's construction or destruction. If people in that area normally date documents this way, the get is acceptable; if not, then it is invalid. The universally accepted Jewish practice has become to date gets from the time of creation or based upon the reign of Alexander the Great, which is used for legal documents. If one dates a get based upon the reign of a modern kingdom, it is only valid if written in a land ruled by that kingdom.
Hilchos Geirushin 1:28
Let’s say that a man tells two others to write a get, sign it and deliver it to his wife but things get delayed for a few days or years, or the get was found to be invalid and had to be re-written, as will be explained in chapter 2. In such an case, the date and location where the get was written are recorded in it, not the date and location where the husband told them to write the get. Accordingly, if the husband instructs them in Jerusalem in Tishrei, but his agents are delayed and don’t write it until Nisan when they’re in Lod, then the get must reflect Nisan and Lod. The same rule also applies to other legal documents.