Very well could be the original plate. Even in bigger districts, the yellow xxA series often lingered around for long enough for 1986-1994 (or even the 1994-2001) type yellow plates to exist with that letter combination. Some districts were so slow that they got yellow 1994-2001 type plates with just two letters! I've spotted at least 2 two-letter 1994-2001 plates, both from the Rychnov nad Kněžnou district (RK). Example here: https://platesmania.com/cz/nomer19512197