I just finished a charity ride and found that the brand new jersey bought for it has a hole in the back center pocket. It is neatly cut, with stitching around it to prevent fraying, so I'm sure it is a feature rather than a defect. What is the intended purpose?
I remember that decades ago when wool cycling jerseys were common, the middle pocket in the back sometimes had a button and button hole. You could button the largest pocket. I don't remember if the other pockets also had buttons and button holes. My guess is that the stitched hole is a vestigial button hole from an old jersey style.