This is a matter of interpretation of compliance. Technically the standard ASTM F696 requires polyester thread. In talking with historical members there are two opinions:
1. Poly thread was determined to be stronger than cotton thread and made gloves last longer (this is fully substantiated).
2. Some believed that poly thread would release the leather as it would shrink in the arc and provide more protection
Opinion 2 has been disproven with test data.
Some believe that using Kevlar or Twyron (para-aramid) thread supersede the protection and wear vs. polycore thread. The manufacturer and end user must agree to accept that or seek a certification body to list or accredit the requirements.