I believe that Speaker of the House doesn't have to be a Congress member of the House. Though I don't have an example of one who wasn't.
Correct! The Speaker does not have to be a sitting member of Congress. You can also be Pope without being a priest...
Don’t think either have ever happened.
Speaker of the House does NOT have to be a member of the House of Representatives or any elected official at all. It has never been otherwise (I’m fairly certain), but there is no Constitutional requirement that Speaker be a representative.
Even if a former “class” in the House of Representatives passed a requirement that the Speaker be an elected member, such a requirement can be eliminated by a majority vote of the current “class”. I don’t think such a requirement has ever been addressed.