@Patrick-and-Karen0 @Stephanie
As far as I'm aware, there is now an extra 5% fee on top of the 3% for new Plus listings, at least in some markets. Earlier Plus listings were offered the lower rate, as part of the Airbnb Plus Advance Incentive Program, in order to get the initiative kick-started. I think it was around the autumn of 2018 when Plus arrived in Nashville so it does sound from the dates you mentioned as if your regular 3% fee for that has been grandfathered in. It may or may not be the case everywhere, but I do know that newer Plus hosts in some Florida markets, for example, are now being charged the full 8%. May be different in Nashville, but I'd say that's probably unlikely.
Best of luck, whatever you decide to do ;))