Others are: Watchtower, Smugglers and Possesion all mention "buys or gain" instead of "gain"... Obviously they didn't know gain always (when not tradered) happens after buy, and as players, we didn't before Hinterland...
The rule book actually made a severe distinction in german between "gain" and "buy", claiming that "gain" happens only during your action phase. They didn't correct that until Hinterlands.
Not the most horrible mistake. (Except they made the mistake of thinking it would be a good idea to "correct" the original rules.) But then Royal Seal and Trade Route should also say "buy or gain".
What do RS and TR say now? Aside from a few edge cases, saying" buy or gain" is redundant. It only needs to say "gain", and that's how the English versions are worded.
Yes, with the English rules it's redundant. But as Asper writes, the Germans changed the definitions so that gain only happens in the Action phase, and then changed a bunch of cards to reflect that. So I was saying that to do that consistently, you also need to change RS and TR. Then it would
mostly works as intended, until Hinterlands, except maybe for a few edge cases (and maybe something major I'm not thinking about). And of course Horn of Plenty is before Hinterlands, and gains in the Buy phase.