Here's a brilliant review on Amazon
that seems to finally clarify EXACTLY what is included.
So it seems like if the track was in fake stereo it has been replaced by the true stereo version. And if the mono version was a fold down of the true stereo version, it has been replaced by the true mono version. If the track was in true stereo or mono and then had effects added (eg. reverb) it seems the majority of these are
included (not true in the case of several tracks on The Beatles' Second Album). The mono versions of She's A Woman and I Feel Fine on Beatles '65, for example, clearly retain the reverb when compared to the 2009 remaster. The reverb is not on the stereo versions of the tracks on the same album as they were fake stereo, and as such were replaced by the UK stereo mixes.
However, in the case of stereo versions of tracks taken from the UK Help! and Rubber Soul albums, they have elected to use the 1987 remixes as opposed to the original 1965 mixes (surely it wasn't that hard considering they're freely available in the Mono set).
The real kicker is on 2 albums (A Hard Day's Night and Something New) we get 3 - yes 3 - copies of the same extended mono mix of I'll Cry Instead. Value for money indeed