Krause isn't always consistent in what level of change produces a new code. In this case the addition of “a” on the end doesn't seem to match the Krause standard as the metal is reported to be the same.
The arms on the coins are different. The difference in the horse is most obvious to me, and the upper right. The arms on N#9488 are also smaller.
The coins were also produced by different mints (so the second has privies) but that doesn't always trigger a new code.
From my view either the arms difference or the mint difference would cause them be two collectable varieties, and I consider the arms design difference to be worth at least mentioning in a catalog.