I'm noticing that myself, but I've used a B13 on my B14 engine, and a remaned B14 on my B13 engine with no issues either way. It appears the casings may be different, but the connection, mounting, and output amperage are (generally) the same. I'll take a peek side-by-side on two I have in my garage and see if I can get a better answer from that.
I know a few guys here should know the answer off-hand, hopefully one will chime in soon.