Chances are that you were doing TSD, however not 100% as Pyung Ahn forms are used by Traditional TKD - Chung Do Kwan (according to that site) as well as TSD and Chun Kuk Do (plus alot of Japanese and Okinawan karate)... Best bet is take a look at your old certs or try to find your old instructor, his lineage (a club/association with him in it as part of their lineage), etc...
My GM history is hard to follow, I have read where he came to the US in 1957 TSD/MDK, yet he had karate on the windows, called it taekwondo in the school, the older students called it MDK. He was friends with the General from the Korean War so he join ITF, then when the general wanted relations with North Korea he quit the ITF. He was a signature for the US to join WTF pictures of that and was the head coach for the first American team to South Korea in the early 1970's.
From all the information I have gather, Jack Hwang was teaching TSD/MDK in the early 1970, and was just calling it Taekwondo
The forms I learn were Pyung Ahn and Plagwae, is the best proof I was taught TSD/MDK and not TKD/MDK.
He may have taught Taeguek and other TKD forms after I left, he also may have drop the MDK name after I left his school.
Jack Hwang has passed away. Now his school is called Jack Hwang's Martial Arts and they teach Taekwondo. No mention of MDK.