1) NPC Journal 82 - Large Pot - Grade 4/5
2) NCC The Caver 5 - Marble Steps Pot Area Survey Gregareth - Grade 5b
3) NCC The Caver 6 - Ireby, Rift-Large, Low Douk and Marble Steps - Outline plan
4) Northern Caves Vol 3 - Rift Pot, Large Pot System - Outline Plan
Number 2 looks like the best. The levels of Necropolis are very different to the earlier NPC survey, which could be the errors PitLamp refers to
Numbers 3 and 4 look identical except that (3) also includes Ireby Fell Cavern