I believe you’re right because ‘h’ in history is pronounced. I read a lot of older texts that use “an” before history/historical. I did some digging, those words were pronounced “istory/istorical” without the ‘h’. So that makes sense. It’s confusing because I have to read a lot of older sources and though the rules have stayed the same, the pronunciation of words have changed. I believe it could still be acceptable to use “an” though. I need to look at at Oxford English Dictionary.