Description (more info)
Types A-O are significant and only should be used when the party encounters monsters in volume. Types P-V are usually found on individual monsters. If your dungeon stocking indicates treasure in a room without a monster, use the Unguarded Treasure table for the relevant dungeon level.
When generating a lair for a monster, it should contain at least the number of monsters of the type given in that monster's "number appearing in wilderness" entry. If the lair contains too few monsters to be in the "number appearing in wilderness" range, reduce the treasure in the lair proportionally—and, likewise, increase treasure in lair proportionally to increased monster density in the lair.
Check what treasure type each monster has HERE.