This even got me thinking. You could imagine that if you were playing some games fairly frequently, you would like to have another copy for the collection. Sadly, that's not the case. These are the games I have multiple copies of.
- AD&D1 PHB
- Menzter Basic D&D
- B/X D&D
- Rolemaster 2nd ed. Character Law/Campaign Law
- Savage Worlds Explorer's Edition
- DragonQuest 2nd ed.
Well, one session of AD&D, two or three of B/X D&D. Yes. That's it.
There are some games which I have played and for which I have multiple copies. Oddly enough they are all just different editions. Looking at that list you find games like Stormbringer, Fading Suns, Call of Cthulhu, Mage: The Ascension, Tunnels & Trolls and Traveller.
From that list I have played FS once, CoC multiple times, Mage a few sessions and T&T I've played a lot and still do. Stormbringer even used to be my main frpg. But, the games I have multiple copies of the same book are games I would like to play, but haven't. This realization made me sad.