You're not really going to find anyone here that is going to know what was changed on those hardware revisions of that card. We'd have to talk to developmers for that card to find out, but that may be a premature action at this point.
What is causing your calls to fail? If you aren't taking L1 errors on the card during your call issues, then I wouldn't worry about the hardware revision of the E1 since everything else is done in software.