I would imagine with that being a single-mic
bedroom recording (if the apocryphal tale is true) that the note durations were
counted off by Harry giving hand signals to the three ladies, as the click of a
stopwatch would have been noticeable. It's actually kind of surprising
that the note lengths are as close as they are. Have you ever timed the
master note lengths and seen what kind of variation exists?
Each recording is not a precise 8 second take so some stop early and some go on longer.