So your GM may teach TSD, but called it Taekwondo.
I maybe wrong but I think my GM taught TSD /MDK, but called it Taekwondo
Very easy to determine. What forms did you learn?
I have read he found the wooden book in 1957 and then stared changing Tang Soo Do Moo Duk Kwan.
He didn't find the book. It was in a museum. The story is interesting, but it seems unlikely that it could have changed the art all that much. I have a copy. It's like <1% about unarmed combat.