What is the difference between D&D 3.5 and D&D 3.5E? If there is one.
"D&D 3.5" and "D&D 3.5E" are the same thing: the "E" is something fans use to mean "Edition". It could be mistaken for a revision letter (as in Revision A, Revision B, ... Revision E), but it's not.
The official name of the game is "Dungeons & Dragons v3.5". It followed "Dungeons & Dragons 3rd edition", which was often abbreviated "D&D 3e". When the revised v3.5 edition was released, fans had to figure out how to abbreviate it and two ways became common, which is why both "D&D 3.5" and "D&D 3.5e" are used today.