I know prior to and during the construction of the Kukkiwon, the building was referred to as the "Danhan Taekwondo Hyophwe Choongang Dojang" which as you say was translated into "KTA Central Gymnasium". But I always thought that by the time the building actually opened, the name Kukkiwon had been decided upon. Perhaps it was a mistake to make that assumption. I tried to look up the answer in the old Taekwondo Gyegan magazines (the KTA magazine started by Dr. Un Yong Kim) and the closest I could find was in the March 1973 issue where they refer to the building as "Kukkiwon". Flipping through the old magazines, I found some interesting articles on taekkyon, specifically baekjae taekkyon, as well as an article on GM SON Dukki. I'll try and scan it can email it to you so you can have it translated. Probably some good information in there for your continuing taekkyon research. Also amazing all the people visiting the Kukkiwon back in those days, people like GM NAM Tae Hi, GM SON Duk Sung, etc.