External Drive With Every Version of OS X/macOS Is it possible to install every version of OS X / macOS to a bootable thumb drive/external hard drive so you can boot off of it?

edit: so I'm ignoring PowerPC stuff because it is rather old now.  Also my main question wonders if the max number of partitions could be an issue.
No. Newer os want GUID partition scheme. Others want apple partition map. 

You can surely put all the images on one drive, just the bootable aspect is problematic.