I am trying to fill out New York State form CT-8 (application for
refund of corporation taxes paid) and don't know what to enter for the
"File Number" at the top, next to the Employer Identification Number.
I have my EIN from the incorporation documents, but don't see a "File
Number" on any of my incorporation docs. This "File Number" seems to
be required on all NYS tax forms, but I can't find anywhere a
description of what it is, or how I find mine.

I have a previous year's tax return which my (ex-)accountant filled
in. Can I use the same "file number"? Is it a static number that is
assigned to the corporation for all time so I can always use the same
number that was used on last year's CT-4 (as filled in by my
ex-accountant)? It's only 3 characters long, so it seems unlikely to
be unique to my corporation... If I can't use the same number, how do
I go about getting/finding a "File Number"?