The game now includes all expansions up to Mondain's Legacy for all accounts (and maybe the 2 tile sets from the anniversary edition that came after- not sure; but that's all that edition was, other than gifts).
Stygian Abyss Upgrade upgrades to that expansion, but doesn't include the High Seas add-on.
High Seas can be added to ML or SA, but works better with SA.
Upgrades don't include game time (only starting out a brand new account does).
There is a trial account available, but trials can't mine/use colored ore, do quests or other things, because they got nerfed from people abusing them.
However, if you have any old AoS buddy codes, 7th anniversary buddy codes, etc. lying around, you can use one of those to try out the full game at the ML-upgrade level for their duration.
Frankly, you're better off re-upping the old account for one month (which will put you at Mondain's Legacy), then deciding if you want to spend the money to get upgraded to SA, and whether or not to add High Seas.
