Yes, and you're highly unlikely to get a 2nd random one. Most of the low-chance drops are from fixed-amount creatures (about 20 of them) plus 3 recurring under Icemist (Demilich x2, Sewer; Greater Demon Elemental Plane of Fire).
Otherwise you need to start grinding a lot of rumour Dragons (all three colours) and rumour Liches.
EDIT: almost forgot, there are some "low-chance" creatures (Carrion Lord, Demilich, Greater Demon, Lich, Lord of the Pit, Merzadan, Saradan) who can drop two Tomes. I'm not brilliant on probability but I think the chance of that is 1 in 250,000 or less.