Two thoughts about the stereo-
1. All bets are off with stereo and the radio. No telling how on-air audio processing might work or was working on an FM Stereo radio station.
I hear an FM station here that jacks up the stereo to the point it changes the mix of the song. That is nothing new, hundreds or thousands of radio stations effectively change the fundamental mix of a recording when they broadcast it.
In the case of this particular station , the interesting part is this sound choice has persisted for years, through different Program Directors. Does this mean (1) strong Chief Engineer presence, (2) the PDs love it, (2) or the PDs are oblivious to it.
Could be a weird feeling for an artist. Thrilled to hear your song on the radio, but unhappy with the way your mix was destroyed.
A friend told me that some producers intentionally keep the stereo down and the essence of the mix centered to minimize the chance of it being ruined downstream.
2. As well known and discussed by many, early stereo versions may not have been mixed by the original producer, or have technical or track sourcing issues. Famously, some hit records had voices or instruments added live when the multi-track tape was played back and mixed to the mono master tape. Since this happened in the moment, it only exists on the mono master tape, and would not have been available to someone doing a stereo mix later. A give away is if you hear something that sounds dramatically different than the rest of the song, such as crisp percussion on an otherwise muddy song. Just one generation for that part, compared to the four track that may have been bounced to one track a few times along the way.
And back then, sometimes much of the "magic" was the EQ and compression/limiting chosen by the disc mastering engineer, for the mono 45. Much of what is/was heard on stereo FM is not the sound of the original 45 mono or 45 stereo pressing. But you knew that...
btw- I think the Hitsville USA set may the the definitive You Tube available sound of the original Motown 45s.
This link should lead you to a poster who kindly uploaded songs from the set.