Stats
Every ability stat: where a training point still pays full value, where it pays less, and where it stops paying.
60 and 90. Speed, Acceleration, Dribbling, Tight Possession and the four accuracy stats (Finishing, Low Pass, Lofted Pass, Heading) share one curve with two bends: points below 60 do little, 60 to 89 pay the most, and from 90 each point is worth about 40 % as much.
Steps. Some stats work in steps: nothing changes until an exact value, then a whole tick or tier at once. Stop one point short and those points buy nothing.
99 and boosters. Skill boosts stop at 99. Boosters are added after, up to 120. Above 99 a formula either stops dead, keeps counting in full, or counts at a reduced rate. Each stat says which.
Ticks. The match runs 27 ticks per second, so one tick is 0.037 s.