Believe the OPer is asking for the differences between the series noted in red.Copied from Wikipedia:
Volkswagen's ubiquitous 1.8 T engine, wholly developed by Audi, also known as the 1.8 20vT, has seen many improvements over the years, and lots of use in several vehicles, sometimes mounted longitudinally, sometimes transversely. Its cylinder head contains five valves per cylinder–a total of 20 valves, and all versions use a turbocharger.
ID code- AGU, APH, AWD, AWU, AWV, AWW, BKF 1.8 litre T, 110 kilowatts (150 PS; 148 hp)
Actually, my APH has Coil on Plug. (Separate coils for each Plug). The coil design has changed slightly in 2001. Mine are still bolt on coils where others I believe are just of the push in type. I am sure there are other differences as well especially with the emissions. More hoses to replaceAnd IDK the answer, we do know the coil set-up changed after the APH to a "coil on spark", facilitating four separate coils.
Mine are still the original Coils and I checked with VW and they never had a recall on the design of the earlier coils only the new and improved onesThe 1.8Ts were always coil on plug as far as I'm aware. Same setup as the VR6 motors. The only thing that happened was an updated design to keep them from failing (time will tell if they hold up better!).