Here's my understanding of artisan skill ranks:

-We have a limit of 1200 ranks
-Mastering cobbling or fletching counts as 500 ranks
-Mastering crafting and two weapon types counts as 500 ranks
-Mastering crafting and all five weapon types counts as 1000 ranks

What I haven't been able to find out is:

Does each individual mastered forging skill count as 166-167 ranks?
Or is there some kind of behind-the-scenes coding where the number only gets divided after a set of three skills is learned?

Where this would matter is if someone is a master of crafting, two weapon types, and either cobbling or fletching. That leaves 200 ranks, so if each forging skill counts as 167 then the leftover is still enough to master a third weapon type... but I haven't heard of anyone doing that, which makes me wonder if it's possible.