If the dynoruns are made with the same dyno then the results are ACCURATE.
For example: all dynos run on the X-dyno will be comparable to each other.
Now if a specific factory has it's own standards for measuring the power of their engines then it should be OK for engines that they test and produce.
Although this is not always the case.
"Kemorc"-Novarossi made the P5X to replace the P5 and it had way less power than the older version(P5) when dynoed on X-dyno. Even though they said in their website that it was around the same.
As for the quality of the engines...did you come up with the 3 top quality engines or you saw it in another forum