Even back in the golden era of radio, they had script 're-runs.' The producers of the many of the series frequently used the same popular script and rebroadcast or performed it on a later date (so it's usually the same or very similar script, but actually a different variation of the performance recorded).  Popular scripts, movies, and short stories often appeared in multiple series.
Some collections include AFRS broadcasts (which are non-commercial) to be aired to servicemen overseas. Other episodes may be labelled with EC and WC would signify East Coast and West Coast broadcasts. These are different recordings reacted by the same actors and script for the different network airtimes. Additionally in a few series there are "Audition" episodes which are unaired broadcasts of the first time a series was performed. Many listeners are interested in these specific broadcasts, but if you are not, the beauty of digital recordings is you can skip the episode with a touch of a button and listen to the next broadcast.