Before the changes to stat training in 1.2, after you've trained a stat to a potential maximum you could continue to train it and it would lead to increasing the potential maximum - which made those potential stat maximums irrelevant, and lead to introduction of new, hidden actual potential maximums that were universal for all characters - 25 for herb training, 17 for Strained Strength training, 25 for crystals of knowledge training, etc.

In 1.2 potential stat training was removed, but limits still stayed - which means that if you have a Strength of, say, 23, and potential maximum of 37 - you can't reach that maximum by training, which is extremely counterintuitive. What's far worse, any Strength draining for that character is irreversible and unfixable via training, especially since those arbitrary limits now use base stat value instead of current value so you can't use status afflictions or items to raise the training bar.

I suggest to remove all the arbitrary limits on training, using potential stat maximums instead.

Also, it might be a good idea to not instantly stop the training once it reaches those maximums, but to slow it down exponentially. This would necessitate renaming them to "stat aptitude", allowing to have base stat values higher than those maximums.
This way if you have a Strength Aptitude of, say, 10, you can still train it to 15 - but it is much, much harder.

One interesting side effect is that potions of Stat or Gain Attributes won't have to raise Aptitudes if the stat is already at maximum.