Well you do indeed learn something new every day , never thought that was possible with a record or every heard of that possibility until now. Even googled to make sure you were not full of it, apparently not accornding to one hit at least I have just read..
It was a very novel and unique thing, and not common, so I can understand that you were reluctant to believe it. I would've been too. And I only heard about It through a YouTuber who does refurbishing of turntables and other hi-fi gear.
Though your statement generally holds true anyway, since it was to my knowledge literally only a single set of records and a single print of them for that matter ever to support it.
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There is also Dolby SVA or Dolby Analog with 4 discrete channels (left, center, right, mono surround) which is encoded via Dolby encoder to LtRt (left total, right total).
That kinda works as a pure stereo signal too although it tends to negative phase correlation (compared to LoRo) as soon as you have higher sound levels in the encoded rear channel.
Dolby Analog is still added to Dolby feature film copies as a backup in case the digital stream fails.
Since it was pretty easy to include two (encoded) analog audio tracks to VHS or other two track systems it became very popular on a consumer and brodacaster level.
Side note: The term 'LtRt' is also used for encoded Pro Logic (I, II) though it's technically not the same.
I might be wrong but I think Pro Logic II supports up to 8 channels (7.1) encoded in only two channels.
Sorry in case this is too off topic.
Don't know about the rest here, but for all I'm concerned, please do go off topic some more. It's all good knowledge and good reads come from it, so cheers, mate.