Your findings seem conclusive with i guess "official" guide https://www.guidetofm.com/players/ability
What i find a little bit dodgy is that attribute cost that a player must "pay" in it's CA is determined by the player role.
So if you take a striker and start training him as defender, his is going to value tackling as more expensive attribute and it would cost more to increase tackling since his training in defender role now, as it would normally cost him if he was training as a striker.
So in other words it would seem that you would want to exploit it somehow. You should convince the game that your striker is actually a defender, while training his finishing through focus and through sessions so he increases it more easily for less CA.
But then again how would it work since every attribute that player has has already been paid for by his 'CA' so if you start a striker on a defender training his 'CA' should actually change almost instantly since now he is supposed to be a defender and has a lot of finishing which should cost very little of CA for defender.. etc.
It's all super confusing.
Also what i find confusing is why some players develop and some don't. And i don't mean that some have different ambition, and professionalism. I mean i have in-game editor and i can see that player is 20yrs old has 165PA while his CA is 130. And he has cca 10 professionalism and ambition. Didn't have any major injuries, has good playing time in the first team but just stagnates. While other similar players seem to grow.
There are so many questions...
Is increase from 9 -> 10 in tackling as expensive as from 19 -> 20.
Can any player train any attribute. for instance if given 100ca/pa player and train him from age 15 to 25 in speed, can he go from 5 to 20 in pace in acceleration ( and decrease everything else).
Is going from 100 to 101 CA as hard as going from 150 to 151 CA. Does PA play a role in it. Does coaching player a role in it? For instance if i have 1 star coaches can my guy of 50CA and 70PA go from 50 to 51CA. Can a guy under same coaches progress from 150 to 151 CA given he has 200PA?
How does age play a role in it. (the official guide seem to mention late bloomers) but there doesn't seem to be hidden attribute in the game that would govern at which age some one should "bloom").
Does a league make a difference? Can a player reach his 180PA in first Columbian division the same as in premier league? Or it doesn't matter he just needs to trigger his "played 60 minutes in first team in first league quota".
Does coach suggestions like "needs to work on becoming more consistent if he is to develop" or "needs to work on his decisions to progress further" mean anything. Or is attribute progression somehow tied with each other.
So much is unknown :|