fancy overlays

so i am looking at some white faced gauges and the break down is 87-90 for one set and 91-96 for the other. At one point i am sure i swapped a newer cluster in mine and it works fine, mine is a 89. so what is the difference between the years. they look the same.

If I remember right the 90- and 91+ aren't interchangeable due to the speedo going from mechanical to electronic and the fuel gauge input being reversed.