The second editions of the main set and Intrigue let me fix up the two most popular products. All these early duds, replaced by real cards. It's an issue with Seaside too, but some of the duds there were cemented in. It's less of an issue with Prosperity though I could certainly patch it up some; Alchemy would rather not exist than get more work put into it; and then Cornucopia and on don't have nearly as many duds.
For the other sets, we fixed up the layout and some wordings. Why do this? Man. It was a ton of work and mostly just means, I can feel better about those sets. We were doing fine with the awful layout and not-as-good wordings versions. But, whatever, some sense of wanting the expansions to be better, they got fixed up.
We were able to replace cards in the main set and Intrigue via selling the new cards separately in the update packs. That doesn't work with just replacing e.g. Rebuild. Possibly we could have had one update pack for all other sets; I'm sure some people would have complained, "hey I bought the new Dark Ages but the old Hinterlands and now to get this replacement card you're making me re-buy something, you suck so hard, boycott boycott boycott." I'm not sure how bad it would have been. It's a classic "this is why we can't have nice things" situation. It would be great to replace just any specific cards that want replacing; some people would hate us for that; we get less hate by having the inferior product. It's a bummer, but I can't change human nature.
At the same time I feel like we got away with e.g. the Masquerade tweak. Not without zero complaints, but you know, it wasn't so bad as to stop us from doing that again. So conceivably someday I'll decide, man, I have to fix Band of Misfits / Overlord / Inheritance. They would usually play exactly the same, and some people would be enraged that they'd have to buy new copies of those sets if they wanted the new wordings printed on their cards, but I think it could happen. Empires just got reprinted though, and I did not change Overlord. So, it's not happening today.
If it had been okay to change cards willy-nilly, I would have changed a lot more. Lots of little things. Like, Mining Village should be e.g. "at the start of your buy phase, you may trash this from play..." Those changes weren't possible because they'd need update packs, and those update packs would be awful products. I don't need to rule out this stuff ever happening, but well, it would require some big shake-up, I mean as it stands it's "put in lots of work, enrage players (have a better product)."