The reality is that the common meters, while better than nothing- do not have the sample rate to give consistent real numbers. Some cans meter significantly lower than they actually are, and some meter louder than they are. Systems that are precise enough to give real numbers with all can designs are very expensive- far above what almost all companies can afford. And for the most part, it actually doesn’t matter the small differences between good cans… as long as you aren’t totally ignorant (or deceitful) and claim impossible numbers.
Ok, so the meters available aren’t perfect- well, the way to deal with those limitations is to recognize when the numbers being given are too good to be true, and not state them. Do larger sample sizes, 10+ shots, compare with known cans sized by side, and test multiple days. Even still- it’s very easy to be 3-6 dB off actual. The problem is people and companies latch onto artificially low numbers (like a can metering less than dry fire, or metering less than the action cycling- let alone port pop, etc.).
Again, once numbers are comfortably in the 130’s- it really doesn’t matter, and people don’t notice the difference in real life. It’s only the internet dorks that argue about 1-2 dB’s, and especially from systems that can’t measure it consistently.