Even in the days of mono LPs, the original master recordings were often multitrack. When that is the case a stereo issue makes sense.
I have a multichannel DVDA disc, "Emmylou Harris, Producer's Cut" which is material originally issued in stereo decades ago. But the masters were 24 channel, and the multichannel mix is great.
Similarly, the recent 3-channel Mercury issues were possible because the masters were 3 channel, but had to be mixed down to stereo when they were originally released.
I have a multichannel DVDA disc, "Emmylou Harris, Producer's Cut" which is material originally issued in stereo decades ago. But the masters were 24 channel, and the multichannel mix is great.
Similarly, the recent 3-channel Mercury issues were possible because the masters were 3 channel, but had to be mixed down to stereo when they were originally released.