Bill, I don't know, but, I would be leery of one that is sewn on. Sure, there could be a valid reason for it being period, but, it is a "red flag." Are you convinced the button is from the period and not a reproduction? If so, it would add quite a bit of credibility to the cap. Like so many TR items with anomalies, it's often impossible to tell when repairs, alterations, etc., were made.