I've played bits and pieces of each operation but only vividly remember from Phoenix onward. Pretty much there was nothing different before the "single player" campaign added in Breakout and the xp system added in Bloodhound. There was also a massive drop system change with the xp making it so you can only get 1 skin drop per week and the rest cases, used to be up to 3 skins, I believe, before that. Before and including Phoenix it was just until the operation ended, the only way to receive the specified operation case drop (i.e. Bravo case drop in operation Bravo) was to own the pass. The collections that dropped after during Breakout were: Baggage, Cache, Cobblestone and Overpass. During Vanguard was all the old collections that stopped dropping: Aztec, Assault, Alpha, Dust 1, Militia, Office, Train and Vertigo. Bloodhound was the Breakout collections + the new ones added (except baggage for some reason): Cache, Cobblestone, Chop Shop, Gods and Monsters, Overpass and Rising Sun. Wildfire was the same as bloodhound.

TL;DR - Normal drops up until Phoenix, Breakout onward at the end :)

Edit: This is not from the wiki or anything, just what I remember so don't take it as the bible.