Not only that, but one thing that gms can also pursue is that of alternate universes. Keep some of the same stuff the original had, such as general workings of society or of technology levels, but don't pay attention to important people or events. Simply work out an AU where you can say the following : 'This never happened. Okay? Just accept it. The following events DID happen.'
This, pretty much! I've made RPs and seen RPs where the GM wasn't an expert on the universe, but as long as you agree with your players on what goes and what hasn't happened etc, it will likely work. Also, if you have big fans joining, utilize their knowledge to improve the lore and RP, don't feel bad in case they know more than you. You're still the big cool organizer of the whole thing and have the last say :3
Truthfully though, there have been times when I've wanted to do a Star Wars or World of Warcraft RP but felt like I didn't know enough about the world to handle it haha... Which is a bit weird because I really love Star Wars and even though I'm not THE deepest fan ever, I still know a lot. Played many games around it and even read some books etc. But yeah, maybe it differs between fandom to fandom also, Star Wars is huge haha.