When Edward Carrington brings the maps to Cleo's ranch house Cleo lights a cigarette, smokes a few puffs, and flicks the cigarette away, but the cigarette reappears for a few seconds in the following reverse angle shot.
On race day in Buenos Aires, some shots show the infield as puddled from rain to varying degrees with the track showing the effects of a recent downpoor, while other shots show both relatively dry.
When Cleo plays roulette, the croupier calls, "Nineteen red. Quatorze rouge." Nineteen would be "dix-neuf." Quatorze is fourteen.
When Donovan, Brash, Ivan and Mrs. Brittony conspire against Cleo, the calendar Brash consults says that August 17, 1934 is a Saturday. August 17 fell on Saturday in 1935, the year the movie was released. In 1934, August 17th would have been on a Friday.
After Colton loses all his money and more at a Buenos Aires casino, he goes outside to the garden to shoot himself. He crushes his cigarette on the ground with his foot but as his foot pivots on the butt, the "grass" tellingly moves with his shoe, revealing it to be an artificial Astro Turf type rug in an indoor set.
Winslow is wearing elegant racing clothes at the track like all the other gentlemen. He would not have been wearing the hat he has on with that outfit.
Anybody who's been to the English Derby race would not say "Derby," they'd say "Darby."