The Fatigue Security Blanket

CTL and TSS, TSB are a function of whatever you've set your FTP to in the software that you're using. As you get fitter, it's like kilojoules burned: It is a relative metric, not an absolute one. Just look at how much more work you're doing from when you first started to where you are now will also give you a sense that you are potentially still getting a lot fitter and faster.