"12 in a set" is only referencing real world toys, nothing within the game itself. Also, the rumor that you stated, about the soldiers at Fort Condor, is quite obviously false, as are countless other rumors about FF7, especially when they are about unreachable goals in the game. People like streching thier imagination, and sometimes people don't know if that is what they're doing.

Also, to comment about the materia issue, I agree there should have been some materia for every element(and poison is an element, as it is in FF8), but, as Big D said, there were already enough materia and having materia for every element just didn't seem needed. There are still ways to use wind attacks and water attacks, so it isn't a very large problem.