It's probably considerably less than that, very few of the early alphabet sequences (say A to M) are still on the road, people have long since got rid of them, so all you see are later combinations.

Once dealers started issuing plates it was much easier to just get new plates than transfer your old one when buying a car, so here we currently have way more plates starting with W, X, Y and Z than we do A, B, C, and D.

Once they get to 999 ZZZ they will go to 00 AA 00 so airport codes won't be seen for a very long time again.

The neighbors have PDX on one of theirs