I was under the impression (and Wikipedia seems to confirm) that all of the pre-Abbey Road records were mixed and released in both mono and stereo, and that Abbey Road and Let it Be are only unique in that they never had a mono release. I have the 2012 stereo LP set (made from the 2009 remasters), and in the research that I did before buying those records I learned that in a series of blind listening tests some experts had difficulty telling the difference between the original releases, the late 70s mobile fidelity LPs, and the new remasters. Surely they’d have been able to tell the difference if the original releases were duophonic rather than true stereo (as some seem to be suggesting).