I think wipple is referring to the release number (along with the part number) printed on a sticker under the phone.
The release number is essentially a production code. It is used to document changes to internal components and such other manufacturing things; the look, feel and features of the phone are the same.
The release number can certainly indicate hardware incompatibilities. However, I don't recall that there are any with the Nortel T7316E. (It is different with the Avaya T7316E, though.)
I currently have a few Nortel T7316E, release 01 through 05, and they all work perfectly.