What's cool about these Beatles albums is that they're not just remastered they're actually remixed. Big difference.
So they're remixed and remastered.
This kind of stuff fascinates the hell out of me
"
Before deciding on the title Please Please Me, Martin considered calling the album Off the Beatle Track, a title he would later use for his own orchestral album of Beatles songs.[27] The album was recorded on a two-track BTR tape machine with most of the instruments on one track and the vocals on the other, allowing Martin to better balance the two in the final mono mix.[22] A stereo mix was also made with one track on the left channel and the other on the right, as well as an added layer of reverb to better blend the two tracks together. The two tracks generally divided the instrumental track from the vocals, with the exception of "Boys", in which the close proximity of Ringo's drums to his vocal microphone placed the drums (but not the other instruments) on the vocal channel.[citation needed]
Two tracks, "Love Me Do" and "P.S. I Love You", were only mixed for mono for the single's release and no stereo versions were ever made, so, for the stereo version of the album, during the mixing sessions on 25 February 1963, Martin created "mock stereo" versions by emphasising low frequencies on one side and high frequencies on the other.[28] These versions would continue to be made available via compilation albums (such as 1962–1966), and on Mobile Fidelity Sound Labs' half-speed mastered vinyl releases (catalogue number MFSL-1-101)[29] sourced from EMI's original stereo master tapes, until the Beatles' catalogue was standardised and issued on compact disc in 1987, starting with the first four UK albums being issued in their mono versions. However, when Capitol Records issued the second volume of American Beatles albums on compact disc (The Capitol Albums, Volume 2) in 2006, the same mock stereo versions that appeared on The Early Beatles were included. When the entire catalogue was remastered for release in 2009, the mono mixes were chosen for inclusion on the stereo reissues, and appear on all releases since, including newer compilations and variations." (wiki)
Martin's autobio (about half of which is the Beatles) is full of stuff like that, what kind of microphones worked best for certain scenarios, etc. Huge section about Sgt Pepper, and all the things he'd come up with to create the sounds John and Paul wanted