There's a difference in rules and lore. Players need enough information
to pursue skills which they believe will be interesting. They should not
have to spend months studying something to discover that they'll have to
spend many more months to make effective use of the skill. Take mining
for example. Its obvious that mining will let you mine things. What's not
obvious is that things to mine are very scarce and that there may no
use for the things you mine without investing in other skills or trade
parterships. It was frustrating to get to level 3 mining and have it tell
me that I could build mines with construction skill.
For stealth, the rules should say that this skill will allow the unit to
be unnoticed at lower levels and steal and assassinate at higher levels.
Precisely what level and success rates would not be known until experience
was achieved. If players want to pass around their experience with
tactics, success rates, etc then that's the lore...
In terms of play testing, even more information should be available.