I never did find any functionality, it did look like it was connected, perhaps IFI had plans for it but, as far as I know, it was never used.
I don’t have any sort of comprehensive list but here are some unofficial notes.
The original version had a flat top, the board would have been marked NC1 with a date code of 2009, the case would have been marked NC1 or NC2 (which was a slightly modified NC1, sometimes the NC2 was written using a sharpie), most of the flat top units still around are NC2 units.
The revised version that elevated the VEXnet key was marked A3 on the board with a date code of 2010. I have no idea if there were any A1 or A2 units. There is an A4 version also but I don’t know if it has any functional difference from the A3 version, it was most likely just a minor manufacturing change in the parts used. I have no idea if there are any versions beyond the A4.