One can find some incredibly useful information near the beginning of the SG Commonwealth and Empire Catalogue that most people seem to skip over, instead, going straight to the stamp listings.
The sections that I find most useful are "The importance of condition" on page xv and "General philatelic information and guidelines" on page xxi. This latter section describes amongst other things, the different perforation types.
I have the 2013 edition of the catalogue, the page numbers are probably different in other editions. Clive