Tom,
Maurice Johnson (& later on, Johnny Johnson) leased their sewing machines. Floyd Byrd (That's right: Floyd Byrd) used to perform all of their routine maintenance for these machines. Floyd, owning a full-fledged machine shop, often made parts, etc. for all of Johnson Leather's machines.
I know that Johnson had, on several occasions, different sewing machines. I do "not" know, nor claim to know, if the earlier machines stitch pattern was different. It would certainly explain a lot???
Best, Capt. Chris