These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Brilliance: Marvin Hamlisch' adaption of Scott Joplin's ragtime music may be an odd choice for the the score since they're from the turn of the century and out of fashion by the time of the movie's setting, 1936. However, it was the music of the younger days of older con men like Luther, Walter Gondorf and the other members of the team. The jazz of the more "modern" gangster wouldn't fit.
Which is a nice case of Fridge Brilliance: she seems just the kind of unimportant, tertiary character you'd never suspect of having any relevance to the story. Plus, it makes it more believable that she'd be into a random, shady guy whose name she does not know just for his attractiveness.