Ok, thanks for the replies. I was (improperly, it appears) thinking of CTL as some sort of overarching, objective fitness score....sort of like FTP but more comprehensive. I guess I was using it wrong.

For my indoor workouts on the smart trainer (which has been about 60% of my workouts over the last year, sadly), I use Sufferfest, which adjusts my workouts to account for my periodic testing. So the workouts do progress relative to my fitness, as they should, but when that data is transferred to Training Peaks, TP reads those efforts through the lens of my old fitness metrics. I do wish there were a way to track daily fitness relative to some objective criteria. FTP is all well and good, but I don't plan to do daily or even weekly FTP tests. Probably overthinking this. As team rides and races (hopefully) start again, I'll be able to go back to using those to gauge where I am relative to others and to assess my own progression.