Some closure on this. The amount of data for this memory card really is 70k, but the AccuVote is hitting that stone age 64k limit one one of its internal tables -- namely the voting position table. You can probably see something similar if you have enough precincts with few races/candidates. So, in short, you can't trust what calc size tells you under some esoteric circumstances. Call it a bug or limitation (myself the former), but it unfortunately can't be fixed without raising some AccuVote memory card compatibility issues.
Can we adjust the calculator to at least predict this problem then?