On numbers, the general rule I've been told is to take the number of Players stated and divide that by 5. Hence, it is generaly 1 PHB per 5 players as an estimate.
This is one reason early on I questioned some of the numbers WotC/Hasbro were releasing (and for a while, they cut back on the PR bS they were spouting, and instead of claiming 25 million playing 5e, it was 25 million fans of D&D...letting one infer what they wanted (whether that meant through the lifetime of D&D, or were currently playing 5e, etc).
My thought was that with some of their statements at the time they were claiming 5e was more popular than the Xbox console sold in stores...etc...and brought how that looked and how that wouldn't actually drive businessmen and businesses to invest in HAS when it seemed like they were lying on their receipts and such. So...the wording changed...slightly... (or someone else also brought it up, or they caught it themselves and decided it needed modification...however it occurred, the wording changed just enough so that it wasn't seen as an out and out dishonesty, or possibly dishonesty).
That said, an estimate of 25-30 million players who have at least tried out 5e (in addition to the other millions who played other editions which when one adds everything up...sort of can be assumed near 50 million from what I've been told) means around 5 million copies of 2014 were sold in some way with the 5:1 rule.
The problem comes in when digital versions are introduced. This makes actual numbers in relation to 4e, and the now current 2024 5e (and late 2014 5e) harder to figure out. Digital doesn't follow that same trend and I'm not sure of what forumula may be utilized in that fashion. It may be that they only do a 1:1 relationship with D&D beyond, meaning they only count one as a fan if they have an account and played in a game (in which case a 1:1 relation matches...or would seem to match reality). The problem with that of course is that some of those will be duplicates of those who play on TT as well...so they cannibalize each other for numbers...
Which is why the only ones that probably truly know the approximate numbers buying and playing D&D currently as well as 2024's release are the actuaries (whose numbers are used) given to managers who then drive forward some of the sales ideas in regards to what to put the investments in next.