I think I understand your question.
(Your English is slightly worse than mine, but English, well “Australian” is my only language.)
1. 40% - measured on some modern machines. But the concept is that you should have got into a situation where you need a little less power - eg closer to VY.
2. Most people understand that reducing momentarily below a timed power limit does not “reset” that limit.
EG In a SE using the 5 min “TO” limit for 5 min, then reducing the power for 10 seconds does not “give” you another 5 min TO power.
The “limits” are based on different things for different machines. Often the TO power might be for example heating up the transmission, so after some time, like some “cruise”, you could use it for the next TO.
Some engines require inspections (or more) after utilising the OEI limits (I believe).