You took "the apostrophe replaces the missing letters in contractions" as me postulating that all apostrophes are only used for contractions, which is jumping t

You took "the apostrophe replaces the missing letters in contractions" as me postulating that all apostrophes are only used for contractions, which is jumping to conclusions, IMO. Even if that statement is taken as a general rule, I can't think of any contractions that don't use an apostrophe, and it certainly doesn't state that contractions are the only place where apostrophes are used.