Suffice it to say if he taught your instructor from white Belt to Black Belt "every day" that would be a highly unusual situation for several reasons.
All I know is that my instructor was one of General Choi's original black belt students. That was the official word given by Chung Oh's School on their website under his bio, and I believe it. The timeline fits.
If Taekwondo began in the mid 1950's (under the name Taekwondo) then General Choi must have had at least one school and must have had students he was teaching it to. Choi created his own pattern set and must have taught it to students during this time period. My instructor would have been in his 20's in the 1960's. They both lived in Korea at that time. Both of them would have lived through the Korean war that had just concluded.
Taekwondo gained peak popularity in the 1990's. My instructor was already teaching it in the 1970's! Imagine that. The Karate Kid movie would come out in the 1980's as a popular martial arts movie promoting Karate, not Taekwondo. Bruce Lee's movies promoted Kung-Fu in the 1970's. Taekwondo wasn't even on the radar screen of North Americans in 1970, that's how far ahead of the curve Chung Oh was.
3. You indicated that your instructor may have been one of the most senior in the ITF and all of the Seniors of that generation had martial arts training before joining the ITF or it's pre cursor under General Choi.
I don't know if the ITF even existed back then. To my knowledge, the ITF came later.
4. Original students of the Oh Do Kwan / 29th Infantry division were mostly chosen because they already had a Martial arts background and Nam Tae Hi was the hands on instructor. Only he and the most Seniors trained directly under General Choi. If your instructor 4th Dan in 1973 15 years earlier It would be interesting for him to have been among that group.
I'm just guessing on what his rank was back then. I don't know the progression. Once he came to Canada, I don't know who would have been training him unless it was General Choi himself, because nobody else was here to learn from.
Imagine being Korean in 1960. There's no internet, no YouTube. If you want to learn Taekwondo, it can only happen in a Taekwondo school, of which none exist in North America. General Choi fled Korea and brought his ITF organization with him to Canada. (That was why the WTF was created. They wanted an organization in Korea.) So now you've got General Choi living in Canada near Toronto, and there's a good chance my instructor came with him or followed him over.
Whatever rank my instructor had, he either had everything he needed before he left, or General Choi continued to teach him over here in Canada. According to my instructor, they didn't have 9 degrees of black belt when TKD started. They only had something like 4.
If Chung Oh learns TKD in the 1960's, he comes to Canada as a high level black belt in the 1970's, opens his school in 1973, and the rest is history.
FWIW my history is well known among many Senior USA ITF people and they know I would never claim to have trained under him every day from White to Black Belt.
I think my instructor was unique. Probably the right blend of being in the right place at the right time and being the right age.