Alot of these numbers people are posting are coming from different types of decibels.
There are actually multiple kinds of decibels.
dBV (1 volt reference)
dBU (.775 reference)
dBM (1 milliwatt reference)
These 3 are used measure the input/outputs of amplifiers and the like.
dBSPL (Sound Pressure Level) is the one you should be concerned about when it comes to sound suppressors.
dBSPL uses the 20 log equation
dBSPL = 20 log (Power1/Power2)
On paper we should perceive an increase of 6dBSPL as twice as loud.
It should be noted that this perception can vary from person to person, as some peoples ears have less hearing damage than others
Also we tend to think high end frequencies are louder than low end frequencies, even when they are played at the same dBSPL.
Hence why the lower tone suppressors sound better to us than the ones with higher tones.
ETA - also I would suggest not getting too caught up in small number differences.
Distance from muzzle, temperature, and humidity all affect the measurement.
Also it can greatly depend on the device used to measure. Was it a professional SPL meter that was properly calibrated, or was it someones iPotato in waterproof case?