Consideration as a single
P.S. I Love You was under consideration as an A-side at some point, but Ron Richards, the producer filling in for George Martin, told Paul it couldn't be used because the title had already been used for an A-side previously. This despite the fact that there had been singles issued which shared names with previously-issued singles without legal consequence.
Andy White on drums
The Beatles recorded ten takes of P.S. I Love You on September 11, 1962 with Andy White on drums. Just like with Love Me Do, recorded during the same sessions, Andy White had been booked by producer George Martin, who was dissatisfied with the recently-fired Pete Best as well as the new (and under-rehearsed) Ringo Starr. Ringo was relegated to playing maracas on the song.
The missing master tapes
It was common practice at EMI to wipe the original two-track session tape for singles once they had been mixed down to the (usually mono) master tape used to press records. As such, there are no existing masters for P.S.I Love You.
"It's just an idea for a song really, a theme song based on a letter, like the Paperback Writer idea. It was pretty much mine. I don't think John had much of a hand in it. There are certain themes that are easier than others to hang a song on, and a letter is one of them... The letter is a popular theme and it's just my attempt at one of those. It's not based in reality, nor did I write it to my girlfriend from Hamburg, which some people think." - Paul
"That's Paul's song. He was trying to write a "Soldier Boy" like the Shirelles. He wrote that in Germany, or when we were going to and from Hamburg. I might have contributed something. I can't remember anything in particular. It was mainly his song." - John
"I was originally a music publishing man, a plugger, so I knew someone had done a record with that title. I said to Paul 'You can have it as B-side, but not an A-side'" - producer Ron Richards, on the possibility of the song being used as a single