Likely they are showing episodes that are public domain. Several sitcoms had episodes lapse into PD due to various reasons - usually incorrect or missing copyright notice on their title screens (same thing that happened to the film Charade) or failure to renew the copyright. The US copyright law in force in the 60s required a proper copyright notice. That's no longer the case, as I understand it.
The Andy Griffith Show, The Lucy Show, The Beverly Hillbillies and others have episodes that are PD. They used to pop up on low-rent satellite and cable stations. Now they are all over the streaming universe. I ran across an episode of TAGS on one of these about 15 years ago on some forgotten cable network, but the theme music and background music had been swapped out for something else. I learned about the PD issue on a TAGS forum. Even though the episode itself is PD, the music was still under copyright, so whoever was distributing the PD episodes was required to change out the music.
Can't vouch for the accuracy of this website's listings, but here is a list of the PJ PD episodes, according to them:
https://www.fesfilms.com/public-domain/ ... n/pet.html