I forgot to say that, because our catalogue is visual (there should be a real scan/image for each stamp listed), we do not really need to specify, in the perforation field, redundant terms such as Vertical, Horizontal, Top and Bottom Imperforated, and so on. One should be able to understand by him/herself from the image. It would only create duplicate entries (or, in the best case, an unnecessary separate field).
1) I am not familiar with perforation methods (comb, frame, line, ...), so I will pass this to somebody more knowledgeable. Please mind that SDC stands for Serpentine Die Cut, which is absolutely needed as information (and should not be abbreviated). Same for Die Cut.
2) I do not think anybody would look for stamps by perforation type or even gauge. The reason is that each catalogue often reports a different gauge for the very same stamp, so when you read 11 it could well be 10¾, 10¾x11¼, 11x11½, ... Any search would be highly unsuccessful and misleading.
3) Have we defined a standard yet?
If so, we can soon start to change or merge the wrong entries.
4) Various... hmm... Only some old definitive sets are too messy even for renowned catalogues, that they did not bother to list all different perforations. That is why you will sometimes find 13-13½ or 14-15. Unless we do not show these specific exceptions, people will keep choosing Various. About Simulated, perhaps they mean that perforation is only drawn, so it could just be an imperforated stamp. I never considered this option! It makes sense, though...
So, what standard should we use? Have a look at these:
a) 12¼x12¾ or b) 12¼:12¾ ?
c) 12¼x12¾ or d) 12¼ x 12¾ ?
e) 12¼ x 12¾ or f) 12.25 x 12.75 or g) 12 1/4 x 12 3/4 ?
h) comb12¼ x 12¾ or i) comb 12¼ x 12¾ ?
The one which looks best to me is... (comb) 12¼ x 12¾