Go Ahead, I see those puzzled expressions!
Yes, I can tell if a jacket is assembled by a left handed or right handed operator by the setting of sleeves into the armholes.
Look closely at a jacket, either on your body, or more importantly, hanging in a store. Depending on the quality of the garment, and yes, the quality also indicates the level of inspection during the jacket assembly, one sleeve is set in smoothly, and the other may not.
I admit it, I am a tactile person. I must touch fabric, clothes, and I even run my hand over a nice sleeve setting. It is my form of appreciation when I see care put into the garment make.
The armhole setting is just one telltale. Another is how the sleeve hangs at ease.
Put the jacket on. Does the sleeve seem to follow the line of your arm? If it twists, it may not have been set to the pattern’s ‘notches.’
Next time you put a jacket on, think of the work that went into the jacket, and maybe think of the operator who worked on the sleeves.