From Section 2.2.4 of the USA Fencing Athlete Handbook

2.2.4 How long are Classifications Valid?

Classifications are valid for four years after they are earned. If, after four years, the classification has not
been re-earned, it then reverts to the next lowest letter and the current year. Such change will be enacted
at the beginning of the new fencing season – August 1. For example, if you earned a B in 2007 (B07) and
did not re-earn your B for four years, your B would become a C11 on August 1, 2011. If you then did not
re-earn your C11 for four more years, it would become a D15 on August 1, 2015.