That really confused me too, I suspect inconsistent ammunition. We did test the Full Nelson again on a .308 today and the numbers were in the 130s and didn't go up.  We also tested on 300BLK (subs) and that metered extremely well.

It's not common, but I've tested a few silencers that increase sound as they are fired, usually that's the result of the silencer getting warmer and not having enough baffle performance to sustain sound reduction when warm, and usually it happens over a 10 round string or even beyond- like 15-20 or more rounds deep.  To climb from 132 to 140+ in a couple 4-5 rounds would be really rare to see.

That type of problem is more common with suppressors that only have 2 or 3 baffles than cans that have numerous baffles.  I don't know what would drive that so quickly in a suppressor with more numerous baffles.  Oil, solvent, or water vapor could drop the first round on a 140DB can to 132 probably.  Maybe that happened and it would have just been 140 flat the whole time if it was dry.

Honestly ~140 is good functional sound suppression, and the shooter on a bolt gun isn't going to need better performance.    ~ear numbers will be around 131 and that's well below 140.

The product is probably consistent.  So one should perform like another.