It seems like pandiatonic is applied to Beatles songs with nothing much more than the meaning of not very chromatic.
IMO The Beatles examples I have seen cited aren't particularly good examples.
It seems to me the key elements of pandiatonic are: non-functional progressions and all diatonic intervals treated as consonances.
When both of those things are combined, it excludes...
- jazz extended chord harmony when it's functional like
ii V I.
- modal music (like folk modal) where the harmonization is largely simple triadic
I wish I had notation of the Beatles songs at hand. My impression from listening is it doesn't really show lots of non-traditionally dissonant intervals being treated as consonances. Especially not given the democratic treatment of all diatonic tones being equal.
The Wikipeadia article gets into that particular point. Pandiatonicism is analogous to 12 tone in an equal treatment of all diatonic tones. When listening to examples from Ravel, Milhaud, Stravinsky, etc. I get that sense of all the white piano keys played randomly with the damper pedal held down. The diatonic tones all smudge together. All the edge is taken off the (traditional) dissonances. Harmonically it's soft and static. But it also can sound fairly dense, because one of the techniques is grouping a lot of notes together to "equalize' them.
There aren't strict methods for pandiatonicism like 12 tones music so it's a bit hard to describe it objectively. But these Beatles songs do not sound like those early 20th century examples in terms of a pandiatonic harmonic palette.