Ron, 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.