Lennon dubbed harmonica onto the intro, middle eight, and ending, while McCartney and Harrison dubbed similar bass and guitar riffs to back the harmonica in the middle eight. Take 12, another edit piece, involved adding the familiar vocalised intro, with Lennon singing and thus in this particular take, not playing harmonica. Several other vocalised improvisations were attempted and eventually rejected, before recording ceased. George Martin was satisfied he had enough material on tape to edit the track together at another session, and so the group turned their attention to recording the single's flip side.
With 13 takes and six edit pieces in the can, Martin and engineer Norman Smith literally had their work cut out for them (pun intended) to edit the song together using scissors, tape and twin-track tape copying. The track they edited together on March 14 resembled somewhat of a Frankenstein creation. The final edit was made up of Take 12 (intro with the vocalised 'da-da-da-da-da-dun-dun-da'), and a combination of Takes 8, 9, 10 for the verses, middle-eight, and ending.
It should be noted that the ability to construct tracks in such a manner was greatly facilitated by Starr's steady drumming over multiple takes. Even slight changes in tempo over various takes would seriously hamper this type of track assembly.
During the post-production session, Martin had one final change of heart. He had previously decided the intro would feature the vocalisation/guitar riff intro, omitting the harmonica part which existed on a different take at any rate. However, during the editing process, he liked the harmonica parts on the middle and coda so much that he decided he also wanted them on the intro. Central to his thinking no doubt, was that following the release of ‘Love Me Do’ and ‘Please Please Me’, the harmonica intro would form a consistency of sound for the group's fans.
One of the recording's unusual oddities is the existence of two versions, one with harmonica on the intro, and one without. Actually, they are not different versions, but rather different mixes. The stereo mix on general release has never featured a harmonica intro. According to Mark Lewisohn, the stereo version created on March 14, 1963 had been scrapped by the time a stereo release was considered for a greatest hits package in 1966. (Complete Beatles Recording Sessions, p.86).
This version may have had the same Take 8 harmonica edit piece synced onto the intro, although at this late stage of post-production, and with stereo mixes a minor consideration in Martin's mind, he may just have left it off the intro completely. We may never know.