We have only just released the Steam achievements list (check it out everybody http://steamcommunity.com/stats/365870/achievements/ ).

The client itself is not updated yet - the new version which we will release soon will also support those achievements.

About getting them retroactively - we will make an effort to make it easy for veteran players to be able to easily get all the achievements they should have. (It will most likely require a player to complete/perfect just one new adventure in order to get most/all the needed achievements they should have).

PS:
Steam achievements have no order, they eventually order themselves based on which achievement has been claimed by more players (for the global list) or the order you unlocked them (personal list).

• Edited on 23/06/15