Further, FB's own estimates cover a fairly wide range, but they have little incentive to user lower estimates.
If somebody dies, they won't be counted as a DAU anymore and in on month won't be counted as a MAU.
More numbers in their Q3 earnings reports: https://investor.fb.com/investor-news/press-release-details/...
So, yes FB's official numbers take this and many other factors into account. However, if their internal estimate is say 5%-40% of accounts are fake they are likely to use a number close to 5% than 40%.
But, I bring it up as the proxy for lot's of other similar estimates. I don't know if what % of 'active' accounts in their logs be that 0.1%, 0.2%, or 0.02% are dead, but I suspect they are going to pick a subjective number that makes them look better.
Further, because actuate numbers take a lot of accurate estimates even 'small' biasing of these sub estimates will compound and heavily bias their reported statistics.
AKA, spam accounts may be easy to find. But, spammers may create other fake accounts to mask their 'spam' accounts.