Yeah, the distinction between editions came from a disagreement of how many Pillars/Pends were necessary to have "a complete set". Some said 12 was enough, others 15, and of course 24 comes from how many are in the trainer. So we just developed 3 editions. Since 12 was the consensus for the least amount needed for a set we went with that as a baseline. 12 Pillars/Pends should cover ~90% of the decks you might build, 15 of each would probably cover 96 - 97%, and 24 of each 99 - 99.9%.
And suxerz is right, cards that you can only get by Oracle, money, or tourney/competitions aren't considered in this count.
Fixed the count in the original post. Thanks for catching the mistake.
@suxerz, thanks for the rep. I'm not aware of an offline version, though there probably is one floating out there somewhere.
If you have all the cards (including rare weapons, shards, and relics), and only need to spend the money to upgrade them, I'll go ahead and add you to the list.