I lived in Rhode Island briefly. During that time, I tracked high-number plates of all types available in the state. I was one of a small handful who did. Most of RI's plates are all-numeric and differentiated only by the plate type. For instance, school bus plate 2021 can exist alongside City plate 2021. Makes perfect sense...
Very soon after I left Rhode Island, the state reverted to their previous practice of recycling and re-using plate serials in the AB-123 format. The highest I previously saw was 399-419. After 399-999 was issued, the series should have gone to 200-000...but didn't. Having spent a reasonable amount of time up there, I can safely say that very little that state's government does makes logical sense (see: issuing serial numbers in reverse, and no I don't mean like Virginia once did).
With the re-instatement of AB-123 serial formats in early 2015, the concept of a "high" doesn't really apply to RI plates anymore. You could buy a new car and be issued freshly-made FZ-555 plates, but you might see GZ-444 as soon as you leave the dealer's lot.
It's an utterly ridiculous place, and yet I miss it. Go figure.