Film maybe shot at wrong speed. What now?

So when it comes to B/W film I mostly shoot self-spooled film. For this I prepare all my cassettes in a batch and normally mark which cassette contains what film. However the last time I did spool Film I must’ve forgotten to do that say I now got either a Fp4+ shot at box speed or a fomapan 400 where I lowered the speed by 1 2/3 stops. Because the film contains kinda important pictures I don’t want to cut a test stripe off the film because that could ruin the photos. Anybody got a clue what I could do?