And a proper name is not good evidence of normal usage. "Christmas" is normal use in an older, Catholic method of identifying calendar dates. Americans don't use that method; most couldn't if they wanted to. But Christmas itself is still identified that way for historical reasons -- the word has gone from being an example of talking about the calendar to being an example of a proper name.

"4th of July" is not a method that Americans couldn't use if they wanted to, but it is an ossified usage that doesn't reflect how Americans generally refer to dates. Like Christmas, it is a proper name of limited evidentiary value.