Consult with your attorney about whether the separation date makes any difference for you. If you both resided in the house after that, then the date obviously isn't accurate. But would you gain anything by disputing it?
(Possible gains - if changing the separation date means the difference between 10 years married versus 9 3/4 - would be important re: social security. If he got some big bonus at work earned after that date but before you actually separated. Etc.)
If there's no financial reason to dispute the date, and it's just a matter of him wanting to hurry up the process - I wouldn't fight it. But definitely check with your attorney.
