Asking for advice on the system for a game

I thought that was weird too. Maybe for situational modifiers? So the GM might say there's a -30% penalty because it's dark and rainy. A player with 100% skill has 70% chance and a player with 110% skill has 80% chance. Just a thought.

Actually, it can looks like weird, but when you think about it, there is a time, when using a skill that you can assimilate and master it enough to do something else with that skill.

That's the concept about mastery in martial arts by the way.
You train by copying, understanding, breaking it down, and then recreating.

So having a skill over 100% ... Yes, i can understand.

You mean like using it to substitute other skills that are more appropriate for the action? Like, using something like Martial Arts instead of Performance to put on a dance show? (I don't know the system's skills, but I hope it makes sense.) Or more like inventing new techniques of the skill? I'd really like an example of 100+ skill usage, if you have time! :D

I don't have any on rpgs, but i can think of some in our contemporary world and society.

About martial arts, yes, that's basically Capoeira.

Like how 30 years+ ago, people mixed mathematics and electronics to create computers.
So far, that's probably the best example i can think of right now.

You can also think, in terms of rpg, of skills over 100% as expertise fields, which are more specialized than skills.
Well, it depends on the skills list at first, but when i see the full Shadowrun which has 7 different skills for gun handling (and i'm only talking about guns, no more).

I suppose a 100%+ skill can be interpreted in a lot of different ways.

That's a curious thought about mixing skills; your example makes me think about a game where the "character" is a whole nation, and their skill progress is technological advancement... or something like this. It would be interesting to invent computers in an RPG. :0

And expertise fields makes sense! Like when you have no more basic info to learn, you pick up a specialization. Thank you for explanation!

Percentile system. Everything starts at whatever base values you determine. Succeeding at something grants no advancement. Every time you fail, your score increases by 1%. You learn more from your failures than your successes.

In terms of skills exceeding 100%.- I can't remember exactly how that played out in prior editions of CoC, but with the introduction of difficulty levels in 7th edition, exceeding 100 basically just raises the threshold for your Hard and Extreme Success chances. I'm not sure if it adds anything in a system that isn't using difficulty levels/opposed rolls.

@Santouche
I can't say I like the idea of success not granting experience at all, since it doesn't seem too realistic to me. Though having percents instead of levels and have them grow by 1 is interesting...
Thank you for info anyway, though! And for explanation of CoCs mechanics. :D