I can't speak for other people's experiences, but when in holiday accommodation, I have never been issued with more than one key.
That was a point I raised on a different thread a while ago.
If you share accommodation and are autonomous, e.g., have teenage children, an in-law, or another couple, sharing a two-bedroom flat... how do you share access?
You can always arrange to meet up at a specific time several times a day - a bit of a pain.
Or leave a key at reception - not too much of a hassle if you are in a hotel with an efficient ground-floor reception in a central lobby.
Another solution is for the last person to leave the flat to walk through the village to reception and then the next person who needs it goes to recuperate it from there. That's okay, but on occasions someone treks over only to find that someone else had taken it 10 minutes before.
Or, yet, again, you hide a key in one of those "cunning" hiding places that every burglar's five-year-old could work out.
The point being that a key could have been duplicated by tourists "hiding" a key for an hour or so without any OC "key guardians" being involved at all.
I really don't see why the PJ exlcuded that idea either.
And then there is the bizarre story of a previous occupant family finding themselves with a cleaning lady entering the flat with a key even though they'd left their key in the lock on the inside. At one point, I thought that perhaps there were two locks with keys and the couple had left their key in the wrong one, but that doesn't seem to be the case.