Why different extension on rom files?

I have wondering why there is so many different extensions on the .nes file ???I have figured out that
(U) Is USA
(E) Is Europe
(J) Is Japan
(UNL) Is Unlicenced.
(UE), (UEJ), (JU), (EJ) (Maybe the same rom for all regions?)But i cant figure these out:
[a1], [a2].. (does this stand for alternate or alternative?)
[!] (Maybe a bad rom?)
[b] (I have no idea regarding this one..
(PRG 0), (PRG1).. (no idea..)
(REV A), (REV B).. (no idea..)
(VS) (no idea..)[h1], [h2] (Hacks maybe?..)
[hM02], [hM34],
[hM04], [hFFE].. etc (Hacks maybe?..)[T-Eng1.0], [T-Swed1.0] (Translated roms?)
[t], [t1], [t2].. (Translated roms?)What i believe is in brackets:( ).
If you can answer my questions you are the best!!! ;D

they arent extensions, they're tags. (!) signifies a confirmed good dump, , and I believe you're right about the translated ones. (rev) indicates different revisions (versions) of the game.

https://www.romulation.org/forum/index.php?topic=1359.0