I keep track of my players' seasons with me by their stars as I only buy 5 star players. Over the course of 28 days, I will get to remember them. If they have gone up a star, I will remember.

I agree that you will be able to keep track of their improvement and change in market value, but what does that really matter? Player growth in Top Eleven is somewhat one-dimensional, all youths will develop at a similar rate, which drops as they get older. You can roughly estimate how much they will improve over the season. And market value, I don't think it's necessary to record it as they will definitely be sold this season or the next as my team goes to higher levels and their stars decrease. I will need to replace them with new 5 star players to continue getting good results.