Apparently, at least some shows are offered on a non-exclusive basis. The same show shows up on multiple channels, cable channels or HD sub-channels. Not unusual any more. No conflict.
It's often not too hard to tell which episodes are public domain (somebody didn't bother to renew the copyright on a specific episode). The theme song is still protected by copyright, so for example on the Beverly Hillbillies you head generic banjo music and not The Ballad of Jed Clampett.