Looking at the routes, the A321 "Sharklets" would be operated by A321Ts with the F and J cabins that are generally reserved for the premium transcon routes, while the routes with just an A321 appear to be operated by standard A321 with standard domestic F seats. This is important to those buying F/J. If that is the case, perhaps the code for aircraft type could be made in a way that's more clear/useful to passengers but this could also be how the airline opts to differentiate between the two types in their own internal systems (note: all "speculation" on my end here - I don't know if AA also codes standard A321s that do have new winglets as "A321 Sharklets" as well in which case my above speculation would be off base).