I'm not surprised I'm still getting it wrong; I've just recently figured out I should add them at all. =] In future, I think, I'm just gonna cat them & let somebody better qualified straighten it out.  But thanks for the info anyhow. 
One thing I do wonder is, if the cat comes back red when I use it (cat:general aviation, say), will it come up on the general "cats" page & let anybody who looks know they can fill into it? Or am I hoping for too much? Or should I try to be more specific? (As is, I'm lifting cats from other articles.)