This unwatchable show is chock full of bizarre directorial conceits, which start immediately with the odd notion that Orry-Kelly is 'unknown' despite having no fewer than 302 movie credits as one of the best-known costume designers in Hollywood from 1930-63. Curiously enough this claim is specifically contradicted by one of the first interviewees.
The tale is largely told using shots of the protagonist rowing a boat, for no apparent reason whatsoever; his mother is cruelly reduced to an Edna Everage caricature putting out the washing next to a lighthouse, for some other unexplained reason; there is not nearly enough of the actual dresses, which is the actual point after all; and even the title is wrong. Orry-Kelly dressed women, not undressed them. The remainder is basically the usual unsubstantiated scuttlebutt about Cary Grant, Randolph Scott, etc.
Among many other inaccuracies, David Selznick did not produce Casablanca.