Two Things That Have Led People to Spell Wrong

First, people sometimes spell plurals with an apostrophe. The only plurals that are correctly spelled with apostrophes are some plurals of letters. Examples: mind your p's and q's, PhD's (although this one can be spelled without the apostrophe, I think).

I believe that the reason people might be confused about this is just one word: Levi's. People take that to be a plural but it is actually a possessive.

Second: Since we have--evidently acceptable--spellings such as Grammys, Emmys, etc. People forget the old rule for spelling words ending in y which I was taught in school: Change y to i and add -es. Thus pastries, not, as we see sometimes, pastrys (etc.).