I graduated from high school and even got a bachelor's degree. I've read several books written before last year, and have talked to dozens of people. I've never heard or seen the word gaol. And if I had, I'd probably assume it was "goal" misspelled. I make no assertions of being particularly smart or literate, but only typical.

Yes, but how often do you use it in your vernacular?

Since that's the topic being discussed, then first portion of your statement wasn't necessary.

Knowing the word exists is a different thing than using it in daily speech. I, and I'm sure most people, would be very surprised to hear there are populations of the USA where "gaol" is used regularly.