2 and 3 even, yes - check out the third of UnnamedCharacter's images, showing the missile sprites. Basically, it depends on the number of axes of symmetry in an object. If you only have one axis of symmetry (as most ships do), then you only flip horizontally (or only vertically, if you had a ship that has asymmetric sides, but vertical symmetry). The only objects that typically have two axes of symmetry are missiles, and the only ones that might conceivably have three axes of symmetry would be those round WC2-style mines.
Incidentally, it's funny that the Kilrathi starbase *didn't* get flipped on two axes, because it's symmetrical both in X and Z axes. You'd think that would be something someone would have noticed, given the desperate need to save disk space for WC1.
No, because not all images need to be repeated if you abandon symmetry - I mean, you already have half of the images you need included in the 37. If you open up one of the ship sprite compilations, you can see that the number of repeated sprites (conveniently marked grey) adds up to 25. So, take 37, add 25, and you wind up with 62.