UPDATE:
I contacted another random company online asking if they had a picture of the part they were selling with the number 590534. After going back and forth a bit and hearing my problem, he was able to contact briggs directly and get an answer. They messed up, all these seals are going out with the wrong number on the bag, and there are "correct" seals anywhere in their inventory.
The seals aren't really needed they say. Normally I'd probably just buy the whole valve kit to get one, he said the motor has slightly worse emissions without the seal. This is a mower I'm selling so I'm just going to reassemble with no seal and be done with it!
At least I know I'm not crazy!