Whatever, my “liberal definition” is a Coggan classic power zone. FWIW you are now preaching to the choir. In 2017 when I was doing those rides I’d only been riding a road bike for a little over a year. Didn’t know anything about TrainerRoad, was loosely following Carmichael Training Systems method. Had learned to surf threshold using HR in 2016 - I’ve got some fun 30-60+ minute HR graphs from that time.
Do I know how to walk the edge of threshold for 40-70 minutes? Have you seen how low my variability is now? Do you want me to write a book? 
My rides are posted in the outside thread. Here is an 11 minute pre-field test pacing effort in January with 19W standard deviation Where did you ride OUTSIDE today (2022) - #35 by WindWarrior which is nearly the same as power graphs on my Kickr in Erg. And a longer 32-min pacing effort two weeks later: Where did you ride OUTSIDE today (2022) - #60 by WindWarrior where I flattened the power on some rollers early in the effort, and due to traffic had two power drops. If I look at the last 12+ minutes, after the U-turn, it has 15W standard deviation on flat terrain which is the variability I see INSIDE on TR sweet spot efforts in Erg mode with power matching. Yeah, I got some 30-70 minute efforts at mFTP/fieldFTP, starting from the time I put a power meter on my bike in October 2016. Its why I’ve been contributing to this thread about 1x60’ at ftp.