makes me think different makers/suppliers, same pattern but their own fingerprint, no one probably paid any attention until now, but just they way things got done, to get things done. I do like the rivets.
Here are the belt loop rivets. What about that two seam down the middle of the back? Mine does not have that.
Gustin Vintage Heavyweight Sweatshirt - Natural Rainbow Nep - $119 Rugged 14oz cotton that gets better with every wear. 
Grant Stone Diesel Boot Dark Olive Chromexcel - #395 Goodyear welted, Horween Chromexcel, classic good looks. 
Iron and Resin - Buffalo Shirt - $119 Classic, yet modern. 6.5oz yarn dyed cotton flannel with a warm micro polar fleece lining.
Not often at all. Off the top of my head I can only think of one MC jacket from that era with the seam running from collar to hem straight down the middle— The Kurland I owned and sold off. Some of the Canadian makers made x zips with multi-panel backs too.
I remember when it sold it was the only jacket I’ve ever sold that I nearly backed out of the sale. I’ve never done that and for good reason but I seriously considered it. This jacket is truly peerless in my humble group.
Depends on the decade. 40's-50's typically a #6 (or smaller). 60's-70's you see the bigger #8-#10's. The massive #8 scoville on my Campus jacket (50's) seems like an anomoly and I would swear it's a replacement but I can find no evidence of that.
