DCSS - YASD - All-Rune win denied ... again! (18 of 12 collected)

[tenaya]

With respect for a couple of people who were watching me when I was
doing very well collecting hellish and Pan runes, I decided to
announce the untimely death of Tenaya the Kenku Gladiator.

Thanks for watching guys!

Dungeon Crawl Stone Soup version 0.5.2 (crawl-ref) character file.

803198 Tenaya the Swordmaster (level 27, -45/237 HPs)
Began as a Kenku Gladiator on Nov 20, 2009.
Was the Champion of The Shining One.
Killed from afar by Urafice (67 damage)
... with a great blast of fire
... in Pandemonium on Nov 22, 2009.
The game lasted 17:21:40 (167471 turns).

I had by this time collected 18 runes (of 12 types) and was trying to
find Cerebov and the fiery rune before going on to Tomb and Abyss.

Eventually the 71st (!!) Pandemonium Lord I noticed laid me to waste
with hellfire. I was reasonably certain that I had somehow missed
Cerebov's level and lost the rune but I kept on hunting. I also
started skipping Pan levels if the level had either the "sealed
oblong" or the "statue on the porch" or the "4x4 room with 4 turrets"
or the "rectangle with secret doors".

How likely is it that after 70+ pan levels I still wouldn't have found
Cerebov? Bad luck or operator error?

Is it possible to have multiple Pan lords on one level?