I don't understand how it can be hard to implement Adventures. If dougz can implement Figures in the Sand with 99.9% accuracy because he's bored surely a paid company with exclusive rights to a massively popular board game can implement a card set that is mostly permutations of other cards.
Well there's a lot of stuff to add/change. Depending on how many wrong assumptions they made when coding the other cards/mechanics, it could be pretty tough. The cards that are actually just permutations of other existing mechanics are: Page, Peasant, Raze, Amulet, Dungeon, Gear (assuming e.g. Tactician and Haven are coded correctly), Magpie, Messenger, Port, Artificer, Lost City, Storyteller (I assume that paying all your $ and drawing that many cards is trivial to code), Treasure Trove, Soldier, Fugitive, Disciple, Warrior, and Hero. That's 18 things out of the 58 that are in Adventures. That's not "mostly" permutations of other cards, not by a long shot. They have to implement:
• The concept of Events in general, including making space for them in the Supply area. (Alms, Quest, Save, Scouting Party, Travelling Fair, Bonfire, Expedition, Mission, Trade)
• The Tavern mat. (Miser, Distant Lands, Wine Merchant)
• Calling stuff from the Tavern mat at the start of a turn or when you gain a card. (Ratcatcher, Guide, Transmogrify, Duplicate)
• The much more difficult task of calling stuff after you play an Action without making you click ten million times per turn. (Coin of the Realm, Royal Carriage)
• Duration cards that stay out more than one turn (Champion, Hireling)
• Duration Attacks that may effect players on their turn (Swamp Hag, Haunted Woods)
• Playing cards on other players' turns (Caravan Guard)
• The -1 Card token (Relic, Borrow, Raid)
• The -$1 token (Bridge Troll, Ball)
• The vanilla bonus tokens (+1 Card, etc.) (Training, Lost Arts, Pathfinding, Seaway, Teacher)
• The -$2 cost token. (Ferry)
• The Trashing token. (Plan)
• The Journey token. (Giant, Ranger, Pilgrimage)
• The Estate token, which I'm guessing is going to be an absolute bear to implement correctly. (Inheritance)
That's a lot of stuff to code and test.