What Coredump said......
I get the impression that you are under the understanding that players must play the newest content each season? If this is true, it is an incorrect assumption. Each season, the new players guide introduces the current rules for AL, as well as the new story origin. If any rules change between seasons, those rules must be followed.
For example: In season 1 characters were allowed to choose maximum gold for their class with which to purchase equipment. This option was revoked in season 2 and all new characters must now use starting gear from class and background - this includes new
Tyranny of Dragons characters. Only those characters which were created in season 1 (not just with a ToD story origin) could purchase starting gear using max gold.
Any character, from any story origin, can play any adventure, at any time. All adventures released since the start of season 1 are still playable at any time. If/When a season's adventures are retired the admins will give plenty of warning that this will occur (most likely a full season's warning) - but at this junction, all adventures and all story origins are legal.
You can play any of the following adventures each season:
- Hardcovers: LMoP, HotDQ, RoT, PotA, OotA - and Curse of Strahd (upon release)
- DDAL Adventures: DDEX 1-1 to DDEX 3-13. You can also play DDEX 3-14 to 3-16, and DDAL 4-1 to 4-14 upon release.
- DDAL Epics: DDEP1 to DDEP4 (convention exclusives)
- DDAO (Author Only): DDAO1 to DDAO6? These mods are debuting at Winter Fantasy as we speak, but are restricted-play events.
- DDAL Launch Events: Death House will be the first such event.
Retired: DDEN1 - Hoard of the Dragon Queen, DDEN2 - Princes of the Apocalypse, DDEN3 - Out of the Abyss.
You can still play these adventures by purchasing the hardcovers, but it is no longer legal to play the pdf encounters version of these adventures.