Every so often, a new variety is discovered on recent stamps. I can attest to many myself. Given that catalogues are for a broad audience, I don't think one should expect every minor variety be listed (the Unitrade is already getting quite thick and heavy, and quite adequate for 99% of Canadian stamp collectors). If you check
ebay and some dealers, auctions, you will also find many un-listed flaws,errors and oddities. A forum like the one we are on is also a good place to make your finds known. Eventually, some will make it to the catalogue, but I prefer to keep my own listing, by reading philatelic literature, monitoring E-bays, checking the various journals such as the Maple leaf, the Corgi times, the Philatelist etc...