Thank You Girl was written by John and Paul sometime between February 11th and 28th of 1963 while The Beatles were on their British nationwide tour with Helen Shapiro. Although the song was described by Lennon in 1971 as "just a silly song that we knocked off," they were obviously proud of it at the time and convinced that this would be the follow up to their recent British number one hit Please Please Me. By the time they entered the studio on March 5th to record the song, they were swayed into thinking that their recently written song, From Me To You would be a better choice for their next single. From Me To You was recorded first on that day and Thank You Girl was relegated to the B-side.
Two recording sessions in Studio Two at EMI were scheduled on 5 March 1963 The first, from 2:30 to 5:30 PM, being utilized for recording both sides of their next single. After From Me To You was started and fully completed, Thank You Girl began at approximately 4:00 PM. Six full band takes of the song were recorded with the group playing their usual instruments as well as performing all of the vocals. No harmonica parts were performed on this day. Take six was considered the best.
The harmonica parts were recorded on March 13th. John Lennon was the only Beatle to be in Studio Two on this day since he was the only one needed to perform this overdub. This session started at 10:00 AM with John's overdubs completed around 11:00. Afterwards, George Martin and engineers Norman Smith and Geoff Emerick stuck around until 1:00 pm to edit in the harmonica overdubs onto the previously edited song, as well as constructing both mono and stereo mixes of the song. Since usually only mono mixes were required for songs being issued as singles, they may not have been sure at this stage if the song would be released on an album, which did require a stereo mix. Britain didn’t get an album release for the song in the 1960's so the stereo mix was not released there at the time. America did get treated to this stereo mix on The Beatles' Second Album. Capitol would typically add Reverb to some of The Beatles' early recordings.
This is the version millions of American record buyers were familiar with on The Beatles' Second Album in MONO...
Here's the STEREO version...
And here is how things sounded in the EMI Studio on 5 March 1963...
•John Lennon - Lead Vocals, Rhythm Guitar (1958 Rickenbacker 325), Harmonica (Hohner Chromatic)
•Paul McCartney - Lead Vocals, Bass Guitar (1961 Hofner 500/1)
•George Harrison - Lead Guitar (1957 Gretsch Duo Jet)
•Ringo Starr - Drums (1960 Premier 58/54 Mahogany)