The ones that aren't in styles made by the official supplier at the time are almost always knockoffs. Occasionally you might see a Mitchell & Ness or something, but if its a jersey style you've never seen before, its often Chinese.
I won't buy "knockoffs" if they're just cheap copies of actual legit jerseys, but I will buy them if I see them in a style or pattern that isn't available thru legitimate sources. I've collected about 30 different Wings jerseys this way.
Example:http://www.authenticdetroitredwingsshop.com/mens-authentic-adidas-jonathan-bernier-black-jersey-45-nhl-detroit-red-wings-team-logo-fashion