It is pretty much a bunch of BS. A good friend of mine, Herman Cohen, who passed away a few years back, and was once considered the B movie kind of Hollywood (he produced Berserk, I was a Teenage Werewolf, and many, many more), told me how he used to completely make up his BO numbers. It was all up to him, no one checked on it, there was no Nielsen, or independent organization checking it out, like there is now. All the producers/studios were trying to beat each other to the finish. Plus, numbers were not published and examined like they are today. This started in the 90s. In the 80s, Daily Variety was only reporting the first 20 movies, and they were getting their numbers directly from the studios. Then boxoffice tracking companies like Paul Dergarabedian's Exhibitor Relations started tabulating those numbers. Everything being computerized today, there is no room for cheat.
Thierry