From the same interview:
PS: Considering your short association with The Beatles, your impact was career altering for The Beatles. You took over bass. You were a witness and a participant in the birth of Beatlemania. When you left the group after four shows, your departure changed the group forever. At their next gig, on January 5, 1961 at the Litherland Town Hall, Paul switched to bass [Solid 7] and the band became a quartet.
CN: I wasn't aware of that. I'm fishing in my memory here. But, Stuart was back sometime in [late February, 1961]. The first time I recall them being a quartet was when they got back from Germany the second time which would be in the middle of '61, when they'd done their stint. That was the time when Paul bought his left-handed Höfner. And, from then on, I remember then as being a quartet. From the four dates I played, I think Stuart came back and he must have played some dates [Stuart may have played with The Beatles on occasion, but The Beatles were a quartet, starting January 5, 1961], then they went out to Germany again, and then the next time they came back, Paul's playing bass and Stuart's decided to become an Art student again.