1 - Very common; easily available on ebay, google product search and almost every knife selling website. Spammed with at least 10+ listings on ebay.
3 - Has been around for at least 2 years and are selling reasonably well, with retailers favouring other newer models over this knife.
5 - Knives that are on the borderline of being discontinued or have been discontinued for less that a 6 months
6 - Products from 6 onwards are either discontinued or limited edition.
7 - Discontinued knives that pop up once every few months on the "For Sale" part of forums or on ebay. Still can be found at a few online shops though.
8 - Knives that need lots of researching to find. Not available anymore in online knife shops and pop up (if you're lucky) >4 months for one at a time.
9 - Knives holding this rarity are the shadowy kind. You can't find any information on them at all (not even from online knife shops that have not taken down that knife's product page). If you see one for sale grab at all cost.
10 - The rarest of all knives. If you hadn't been here you wouldn't even have known that it existed. Should you have one of these you better lock it up in a triple-combination safe and treat it like a family heirloom..