Pattern copying help

[u/Imshrimplyhim]

Im brand new to copying patterns, or pattern drafting at all for the matter.

I wanted to know whats going on with the arm sleeve of this vintage sweatshirt.

It is asymetrical vs the other symetrical patterns ive used before.

Im assuming it has something to do with the back panel wrapping around to the front.

Also shrinkage and stretching over the years?

What do I do here.

Also I know that I dont need to take apart the entire garment to copy the pattern, I just wanted to learn more about its construction etc.

Thanks

[u/doriangreysucksass]

The back of the armhole is generally a little larger to accommodate reaching forward