Check out the mono mix of "Lucy in the Sky with Diamonds" again. There is a flanging effect applied to Lennon's vocal that is absent from the stereo version. "She's Leaving Home" is also faster and (as a result) pitched slightly higher compared to the stereo.
As for your question, the only thing the stereo set is missing is the mono mixes. For songs where there is no proper contemporaneous stereo mix (such as "Please Please Me", "P.S. I Love You", "She Loves You", "Its Only a Northern Song", "You Know My Name [Look up the Number]" and the "no tambourine/Ringo on drums" version of 'Love Me Do"), they are presented in mono on the stereo releases. The only instance of reprocessed/"fake" stereo left in the catalog is "I Am the Walrus" which goes from real to fake stereo a couple of minutes in when the radio voice overdubs start and stays that way until the end of the track. The mono "Love Me Do" on Past Masters (as well as on Mono Masters) is actually from a needle drop as there is no tape source left to use as a master.

So, on my way to work I popped one of the CDs into my
car player. Now I realize the car is not the best environment
to listen to this music, but I have a Cadillac whose interior
is quite quiet. The stereo system is also pretty good
compared to most.
The first CD I sampled was SGT. PEPPERS.
I have to say, I was not immediately impressed. Not a
fan that it's mono sound which took a bit to get
used to the fact that instead of being enveloped in
stereo sound which distributes itself across the fronts
and rear, I was listening to solid mono across the two
fronts.
The quality was quite good, but as I went from track
to track I didn't notice anything unusual despite the
fact that SGT. PEPPER was pointed out as being one
of the mono discs that had distinct differences.
It wasn't until I got to the SGT. PEPPER REPRISE
that I heard many things I never heard before. First,
the transition between GOOD MORNING and the REPRISE
is slightly different (the first sound before Pauls countdown).
Then, I heard audience noise I never heard before such as
applause that was far more distinct. Finally, just before the
REPRISE segways into A DAY IN THE LIFE you can hear
some additional background screaming. That was pretty
neat as none of that was ever brought out within the
original late 80s recordings.
Question: If this MONO set is missing ABBEY ROAD
and LET IT BE then what is the STEREO SET missing?











] albums list, Rubber Soul and Revolver have (and probably always will be) tied. I have never been able to decide which I prefer, and thankfully such a decision is not (in any larger scheme) really necessary.
Are Beatles purists disturbed by that release? 
