1,706. Examples of Invalid Gets
Hilchos Geirushin 1:25
The following gets are invalid: one that was signed by the witnesses but not dated; one that was pre- or post-dated; one that was written by day and signed the succeeding night (which is the next day in halacha) – this is the case even if the parties were involved with the divorce the whole time; if the get was written in Jerusalem and they accidentally wrote the location as Lod. A get must be signed at the time it’s written, in the place where it’s written.
Hilchos Geirushin 1:26
If the man cut the date out of the get when he gave it to his wife, or if he didn’t write the exact date, just which week of the month, which month, what year or even just which sabbatical cycle, the get is valid. The same is true if he writes “Today I divorced her” in the get, referring to the date the get came out.