The Petra Zone

I'm one of the music nitwits here, so please forgive me if this is a dumb question...

I have a couple of Petra vinyl singles with one side being mono and the other being stereo. I'm not sure what the difference is. In my limited understanding I would assume that mono means that every speaker will have exactly the same sound, while stereo means that (slightly) different audio streams come from the two different speakers. Is that a correct understanding?

I guess all of Petra's albums have been recorded and released in stereo, so why bother with a mono radio version? What's the deal with that? And if you would transfer both sides of the single to your computer, would it result in different recordings, or does the stereo effect get lost when you record a record to your computer?

Also, I have a couple of cassettes (only cassettes - s/t and Not Of This World) with a small ES symbol. I'm not sure what it stands for, but I found a source somewhere stating that this means Simulated Stereo (why then ES??). If Petra's albums have been released in stereo what's the use of creating a special Simulated Stereo release? Or does ES stand for something else?

Were these 45s or 33 and 1/3's? The latter...likely for radio and mono phonographs in markets outside of the US. When I was in Christian radio, we were mono on LP with mono turntables, mono mixers, etc. I don't know why they would have been pressing mono for US markets in that time period except for 45s.

I know in some areas the radio stations still had some mono record players that were expensive to replace. Plus AM radio is only mono, and FM radio was mono in the early days.

45s for More Power To Ya, Not Of This World, Godpleaser, Grave Robber and Hollow Eyes. 12" for Voice In The Wind and possibly for It Is Finished (don't have that one). All were produced for US radio. The funny thing is that earlier two-sided 45s had stereo on both sides (Why Should The Father Bother?, The Coloring Song, For Annie).