The value of the power check is that it tells you what you need to know in the situation you find yourself in. And if you do one for the aircraft you fly: the source of the values is no mystery
Stand to be corrected, but what is really clever about the power check is that the values work irrespective of DA and weight: that is you need x% torque or x" MAP margin to guarantee a particular
manoeuvre. Depending on your weight and DA, wind etc, you will either have that margin or not.
Again, I may be wrong, but the values should work across aircraft types, ie. be the same for SE pistons such as R22, R44, H269. This is where 3" over hover power for a vertical take off has come from.
I have seen several different lists handed down by instructors to students and many have some form of error or another because the reasoning behind the chart has got lost. e.g Take-off = +1 is manifest rubbish. If you can hover, you can take-off: so hover power is take-off power (minimum for IGE normal hover height). More is nice to have. Lists with values so generous that there would never be an issue with power don't really help define the point where available take-off and landing techniques is limited.
TT