> on all three

Except if you can manipulate the timestamps, then they aren't relevant anymore, so the search space is much bigger than the intersection of each set of days.

It's the intersection of all the people who visited each printer at least once any time.

Yeah, but the police (and then the prosecutors if they find someone who matches) are operating under the theory that the tracking dots are correct. They really want the dots to be correct. They don't want the dots to be wrong. This is why nonsense like "fiber matching" lasted so long: the people prosecuting the crimes want it to be right so badly that they're practically on your team.