The leather trim and strap is calf leather. Calf leather is prone to wrinkling, especially a shoulder strap or anything else where there is pressure applied. Yes, the stitching of the strap pulls it tighter to where it is more prone to wrinkle faster. This could be a reason why they were on the fence with whether they should stich the strap. Don't worry, it's Normal wear. If it cracks, then I would deem it as a defect.