That pressure drop chart above shows the difference between the atmospheric air pressure (1014 hPa while the 2003 was on the dyno and 1012 hPa while the 1997 Type-S was on the dyno, for what it's worth), and the pressure in the entrance of the intake manifolds. Whether you carry out that measurement at pretty much sea level in England or at pretty much sea level on the Eastern Seaboard of the US, the pressure loss caused by the stock intake system in a stock NA2 is going to be the same.
In case you want to see the horsepower and torque curves for the two bone stock NA2s, here they are:
Saying the power at the wheels was "measured" in the second graph is somewhat of a misnomer, of course. Dynos measure torque and multiply that by the engine rpm to calculate the horsepower. If the dyno wasn't calibrated recently, the torque measurement may well be off and therefore the calculated horsepower will be off as well. If the rpm weren't measured from the tachometer pickup loop in the engine compartment or directly from the engine management system but were guessed based on the dyno's roller speed, the horsepower calculation will be based on a guess. Then that calculated result should be adjusted with a correction factor to what the rwhp curve likely would have been had you carried out the run in standard atmospheric conditions. To do that, you need to measure your current air temperature and current air pressure (note: as you can tell by the air pressure measured during the English dyno day, there must have been a high pressure system prevalent on that day) and plug that data into the formula. After all that, you'll have calculated your "corrected" rear wheel hp figures.
Then some dynos estimate crank hp figures based on the rwhp figures. There are various ways of doing that and the results depend on which method you use.
There are so many opportunities for inaccuracies that I really think dyno results can best be compared if they were carried out on the same dyno on the same day and the engine speed was actually measured, not just guessed based on the roller speed. A dyno can be a great tool for tuning engine management systems, measuring the impact modifications have, and comparing cars at a dyno day. But even if dynos are used properly, since so few of them are regularly calibrated, I think the absolute numbers they spit out shouldn't be taken as the gospel, they should be compared to the other numbers the dyno spit out on that day.
Maybe my suggestion for the OP was lost in the discussion but as I stated in my first post in this thread, if he doesn't mind the air filter getting dirty quickly, I'd recommend replacing the OEM intake snorkel with the Downforce scoop and being done with it. He'll get as much "ram air" effect as he can, the path of the airflow will be smooth, the smallest diameter in the intake system upstream of the throttle body will be 3.4", and he'll have a reasonably large filter to keep the air clean with minimal restriction.
If your dyno tests show that the intakes you developed make more power than the intake Comptech developed, could you explain why?
P.S.: If you measure the pressure drop caused by your intakes and by the Comptech, stock, Downforce, etc. intakes you are replacing, using something like a $30 Dwyer Magnehelic differential pressure gauge to carry out the measurement, you'd have an additional selling point.