When Marc Okrand first wrote the name, he wrote it as qeylIS lIjlaHbe'bogh vay' Kahless whom anyone cannot forget. He did this because he WANTED to write qeylIS lIjlaHbe'lu'bogh, but -laH and -lu' are both type 5 verb suffixes and can't go on the same verb, by his own rule. He made a rule that says when you otherwise WANT to use both suffixes, you can use -laH on the verb and then make the subject vay'.
But it's not clear whether this phrase is THE way Klingons say the name or if it's just a common description.
-lu' doesn't mean someone or anyone. It means this verb has no definite subject.
In English, anyone can't forget him isn't a well-formed sentence. Someone can't forget him and no one can forget him are good sentences.
ghaH lIjlaHbe' vay'
Someone can't forget him/her (there exists someone who is unable to forget him)
ghaH lIjlaH pagh
No one can forget him/her (there does not exist a person who can forget him)
You're thinking in terms of formulas. Don't do that.
vay' means someone, something, anyone, anything, somebody, anybody: a non-specific entity.
-laH + -be' means the subject is not able to perform the verb.
So *verb*-laHbe' vay' means there's a non-specific entity that is unable to perform the verb. Now you just have to put that in the simplest terms in English. Translate the meanings, not the individual words.
qeylIS lIjlaHbe'bogh vay' Kahless whom somebody cannot forget; Kahless who cannot be forgotten by anybody; Kahless whom a non-specific entity cannot forget.
As far as no one can, that's just a shade of meaning. There's little or no difference between somebody cannot and no one can. Okrand was translating Kahless the Unforgettable, and has translated it as both qeylIS lIjlaHbe'bogh vay' and qeylIS lIjlaHbogh pagh.
So it sounds like you're saying there are two different translations, both of which mean "unforgettable", and they mean two slightly different things, and while one translation being used implies no one can forget him. The first (and official?) translation means effectively that there exists a non-specific person who is unable to forget Kahless.