The driver init for the 7100 tells Chirp that its memories start at 0, as does the init for the 7000. All of the other radios in that driver tell Chirp they start at 1. When I wrote the code for the 910, I remember initially using the 7100 code as a reference, but being puzzled as to why it started at 0, when the manual says the memories are numbered 1-99. I initially followed suit, but starting at 0 did not work for the 910, which also numbers its memories from 1-99. I don't have a 7100, so I couldn't test, but just wanted to mention that here in case that code really should be starting at 1 instead of 0.
The manual says 1-99, so perhaps this was just an error in the driver since forever. In that case, filing the bug may just end up with that change and a module for the OP to test/confirm.
--Dan