How did MWPP make the Maunderer's Map?

[hutchingslesley]

No: HPFGUIDX 154202

I think the marauders only included areas they knew about and they
couldn't include the Chamber of secrets as they didn't know if it
existed. As there are hundreds of names on the map, Lupin probably
hadn't noticed PP in Hagrids hut as he probably hadn't looked for it
there. I'm guessing that they either didn't know of the room of
requirement or it is unplottable, they made their map based on their
exploits when they had joined Lupin as animagi and probably explored
Hogwarts grounds more than the inside of the castle.???

hutchinglesley