Guinea pigs live very much by scent, and identify themselves by scent. They have an individual scent, but also a group scent. Boars smell stronger because of the testosterone. Piggy noses are much finer than ours!
A guinea pig not acknowleding a piggy they have fallen out with or have been separated from for a length of time has less to do with bad memory than with a missing "us" scent. That's why formal introductions on neutral territory should be considered when a piggy has had an operation and needed to be kept apart (even next door) to the others - it has still lost the "us" scent and is no longer considered a part of the tribe after about 2 days. It is the same problem with two sows after one of them had babies - they need to be formally re-introduced as well, as many just won't move back in as if nothing has happened, even if they were best of friends before!
That's why too many baths are not good - they can seriously interfere with the group identity, and that is the reson why piggies need to go round and scent mark their freshly made up cage.
