Something got me to take a look at my program CDs this morning. And it was an interesting exploration. I found install disks for MacOS 9.2.1 (and another version of OS9 that isn't labeled), 10.1, 10.2, 10.3.7, 10.4, 10.4.5, 10.5, 10.6, and 10.6.2.
The surprises are that I couldn't find any 10.0 or 10.7 disks (I know 10.8 and 10.9 were just downloads), and that only .2, .4, .5, and .6 were commercial disks (the others came with Powerbooks G4 (pismo and titanium), a PowerPC Mac Mini, a MacBook Pro, and an iMac 27" 2009).
Now I'm trying to figure out if there's any reason to keep any or all of them around. I'm leaning towards no.