Hey - the short answer is it’s probably hard to know!
Other people have noted some good stuff, but I’ll just add something from my own experience! After 36 months of riding a lot, going hard etc., but no structured training, got a PM and started structured training with TR in Autumn 2018.
Went from 307w to 315w to 323w over base and going into build. Went back to racing crits in early season that I was hanging on the back of the year before, finding myself able to drive the pace, make people hurt and be competitive in the final.
I think I assumed that fitness would just keep going up and up, and would be at 340-350w at end of the year. This… didn’t happen. I was flying in April, but racing hard crits twice a week, not following proper structure, and crucially not giving myself a proper rest meant I was definitely slower by August and fading hard. I’d been so desperate to use the newfound fitness - when you get these early gains you feel invincible, but you aren’t…
Sorry - just a longwinded way of saying that it can be easy to lose fitness (even when that seems impossible at the time), and that you need periods of rest, reset and time off the bike. You can’t - and won’t - get exponentially fitter.
People have also made good points about extended power and being able to hold FTP: there’s more to fitness than the abstract number. With more experience, I’ve now started to realise this: I’m probably at a similar FTP (325w) to this time last year, but because I have really worked on holding it for extended periods of time, as well as doing so with not too much loss in TT position, I feel much stronger coming into the upcoming TT season.
Best of luck!