I think correction factors are most useful for comparing data on the same dyno on different weather days. Also the more you have to correct, the more potential for error in the correction. Here is an example of why I think correction factors are useful.
You have a motor on your dyno and have it fully dialed in. The pressure is 28.5 temp is 84 degrees humidity is 30%. Customer wants to try an intake manifold modification. Customer returns with the manifold 2 days later and you test his modification. On this day the pressure is 29.5 and 74 degrees and 10% humidity. If you use no correction factor how do you decide losses or gains due to change in weather or change in the manifold? And if you do use a correction factor to account for the change In weather which correction factor will do this more accurately?