...how fast it was...
That would be similar to the practice of identifying people by their initials (not for logins, but in general discussions and emails, etc) which I assume is widespread. Once the company has more than about two dozen staff, you need to start using the middle initial, where there is one. Beyond about 60 staff, even that doesn't work.
To a mathematician in possession of stats about names, I suppose it is another form of the Birthday Paradox. Same problem, messier calculation, but a very similar answer.