Let "old" adventures be available. Whether during a short period where they can be found by explorers or at the merchant for guikd coins or map fragments.
I am thinking about the old 2012 football adventures that yielded a lot of XP.
The 2012 "End of the world" Maya adventure (where i still have 1 left...) that coloured the whole island bloody-red. Maybe there are even more that i dont know.
I am not including the lame "click and recover" adventures from Easter, neighter the newer football adventures/Xmas adv that needed collectibles to be finished.