There wasn't an A suffix. The project that resulted in the 71B never intended to call it 71A. There may have been other designations used during product development before 71B, but as far as I've ever heard, they did not include 71A.
The 75 story is more complicated. The 75 designation was going to be used for two variants, the 75C and 75D, with 8K and 16K of internal memory respectively. However, at release, only the 16K version was introduced, and given the 75C designation. At least one photo of a unit with the 75D designation slipped out.
The later 75D model was not part of that original plan. It was a 75C with the standard 16K of memory, with an added port for a bar code wand.
The 75 had at least one earlier pre-release designation, which IIRC was 1000CX, not related to the later palmtop with that designation.