You are right about the STCW classes, they are now required for everyone as the grandfathering deadline has passed. It no longer matters, but you misinterpreted eligibility for grandfathering, it was if your service began before March 24, 2014. That means service for the endorsement you are applying for, not the start of your career. Since Chief Mate requires one year while holding 2nd Mate, you began your service for Chief Mate on the first day of service as a mate after getting your 2nd Mate endorsement.
You can apply for the national endorsement (license) only, and add STCW later.
James D. Cavo
U.S. Coast Guard
Mariner Credentialing Program
Policy Division (CG-MMC-2)