Wikipedia:
EN 13537 (or EN13537) is a European standard designed to standardize the temperature ratings on sleeping bags manufactured and/or sold in Europe. As of January 1, 2005 a CEN criterion came into effect covering the testing and publication of temperature ratings for sleeping bags. The new criterion differs from the standards that existed formerly. In 2016 this standard was superseded by ISO EN 23537:2016.
So, probably not much.