Hi,
If I recall, the A2620/2630 had the possibility of different RAM configurations. It would have been possible to make one revision of the board, and solder on 2/4/6/8 Megs of RAM. I doubt they sold this many variations. A 4M configuration would allow the A2088/A2286/A2386 Bridgeboards to map their I/O space inside the Amigas autoconfig memory at around the 6MB mark, limiting the maximum RAM you could add to the Amiga to 6MB. So, 4MB on the A2630 and 2MB on the A2091 (a very popular combo as sold by Commodore) and a Bridgeboard installed.
Other accelerator manufacturers like GVP mapped their RAM higher and avoided the 6M "barrier" imposed by CBM for the bridgeboard. I suppose CBM would have done the same had they ever released further accelerators, but then the A3000 and A4000 became the flavour of the day...
Good luck!
-G
