I like to caution the idea of assuming respected manufacturer’s lights are accurate and consistent throughout. I just posted some ceiling bounce results for my AA lights and there are several identical lights from “respectable” companies that show considerable variation in light output. My ceiling bounce measurements have been extremely consistent even when measuring the same light months apart.
Also I prefer we don’t apply our own correction factor and instead apply a standard correction factor among all the lumen tubes. One of the main benefits of so many people owning TA lumen tubes is so we have a standardized basis to compare lumens among members. Even if the lumen tubes are not calibrated to realistic lumens, they are still calibrated consistently among all the units so we need to come up with standardized correction factor.