Recommend, for those in nappies at the time of this flic, check out at least this Part 1 of 4 The Making of A Hard Day's Night ... especially if also have heard of/seen! The Mouse that Roared. This mentioned in intro comments of director, but it's all good.

(Of course I was late to This party, too, having already tuned-out 96% of "pop" material all along.) But to hear the Famous Reviewer™ (at opening of this 'Making-of' recap) directly compare it to Singin in the Rain [!!] ie among All musicals: is also a measure of how clueless I remained for too-many weeks ..months, not hearing enough samples to grok the subtlety (and their mastery.)