This is a really weird and kind of complicated subject. Wish it were a little clearer.
From what I can tell as well, there appears to be no difference in warmth with winter fur - only market value. Since it's not mentioned in the changelog, I'm guessing that hasn't been implemented.
So just checking: even with Fine small knife, Fine fur and Fine cordage... it is impossible to craft Fine fur clothing, right? Because, looking at diy_glossary, all clothing creation uses the common skill and none of the fur clothing recipes come with a built-in bonus but fur cap - which has 15%. And you need a 20% bonus? I just tried about a dozen times with a fine small knife + fine bear fur and only got decent fur caps.
I read in the wiki that Common skill is always base 60. But I read in many places on the forum - here included - it is said that you need base 40 to make fine items. Sooo... what's going on?
Also - and this is the first time this happened to me - I recently made a Fine Raft with a masterwork handaxe and fine spruce wythes. How is that possible?
IS it possible to make fine bear fur clothing with a masterwork knife? If so, then I've really got to find a masterworking smith.