it was indeed pre-"Generations." Walter Koenig made a joking reference to it in a comic book, saying that they'd have to skip Star Trek VII and go straight on to VIII because of it.
The "curse" was basically a joke that came to be taken too seriously.
In the introduction to "Modala Imperative" I believe.
That was 1992ish... but it stretched back to around '89 I believe.
And what's all this about Galaxy Quest? In no way is that a Trek movie.
As others have pointed out, the odd/even "curse" is ridiculous, and something fans put way too much thought into.