According to the folks who presented this subject at IAEI who were behind that part of 110.24 their intention was only to make the NEC tell you that there could be a hazard. As long as you don't open the covers to work anything live that's all you need.
If you were going to get close to unguarded conductors or bus, then then OSHA regulations would require that you do all the math and post the values on the outside.
There's no way that a calculated value will be valid forever...I'm reworking a place now that was first electrified bask when open-front black slate switchboards were considered cutting edge technology. Somehow I would not blindly trust any values written the original warning labels.
It was kind of amusing when we had folks bidding on the work; one guy saw the old board and refused to believe that all of the power for the whole place came through that 'antique'. He kept looking all over the building for "the real main electrical service".
If he submits the winning bid, this could get interesting very quickly.