I first started using T4 on a regular basis back in 1989. T4 opened in 1986. In the early days, there were a few shops, but not too many. As time went by, more and more shops restaurants and bars opened. That part was horrible.
I was often travelling long haul, as the job I had required rather a lot of global travel, and the Company paid for me to travel in either business or First. The Company that I worked for was a top customer for BA. I reached Gold for about 13-15 years. (The only downside of that was that once I had the points to re-new, I immediately tried other airlines, so I did not earn enough for GfL.)
My memoreis of T4 were mainly of the Concorde/First Lounge, which was normally excellent, with much better reds and whites than BA gives you now! I stopped trying the various whiskeys in late 89 after a warning from my Doctor!
Perhaps my memories of T4 are confused by time, but I remember a place which was so much better than T5. It was never as good as Singapore, but nowhere is!