Themes that recur later?

Many reviewers have noted some of the signature Hitchcock touches in the visuals: the sensational opening of the showgirls on the staircase, the overt voyeurism in the theatre, the covert voyeurism of women undressing in their apartment.

But what about some of the story themes that recur in his later work? For example, merging of identities, where people become like their doubles? Early on, Patsy and Jill almost seem twins, sharing a flat, working in the same place, looking and dressing alike. However their different moral characters draw them apart, one to self-indulgence and the other to self-sacrifice.