Why won't topcases for other 14" G4 iBooks work on this machine?

Hi! I encountered x2 of this machine, which is the highest-end 14" iBook, with integrated Airport Extreme and BlueTooth. They both work, however the topcases are mangled and not presentable (although functionally the topcases do work). No problem, I thought, as I replaced them with other topcases from similar models, only to find that the trackpad did not work at all when I tried topcases for 1.33GHZ 14" iBooks on the 1.42GHZ machines. The topcases look the same, the connectors are identical and connect fine, and they power up the machine, only the trackpad is dead. I've tried about x10 various topcases, and only the two I have that are specifically for the 1.42GHZ machine will work. Anyone know why, or how to rectify this? It's a shame that I have two high-end iBooks that work great, but that aren't going to be usable simply because I don't have an absolute 100% match on the topcase. Unfortunately the electronics related to the trackpad can't be moved, due to being embedded in the plastic of the topcase. Thanks!