During opening credits number, Robert Morse and a young fellow window washer board an electric scaffolding in exterior rooftop shot, but by next scene when scaffolding has descended a few floors, co-worker is now a much older man with much less hair.
An exterior shot implies that nightfall is descending on New York City at the end of the workday (5pm). This would indicate that it is winter. However, most of the women employees are wearing short-sleeved or sleeveless warm-weather styles, and the CEO mentions that he plans to play golf the next day.
When Finch reports to work early on Saturday morning, the shadows indicate it is midday, not early morning.
Miss Jones tells Mr. Biggley that his knitting is in the back of his right-hand drawer. But it's in the first place he looks, which is the front of his left hand drawer.
Although Finch's rise to top of corporate world is supposedly pegged to sequential chapters of same-named title book he reads throughout movie, his progress through text isn't sequential - even near end of movie he is seen poring over beginning chapters for next bit of ladder-climbing advice.
In the musical number at the end when the men are singing about being members of the human race, the clapping of the businessmen is on the downbeat but the audio claps are on the upbeat.
In the first scene of Hedy LaRue at the company she shimmies up the stairs in the lobby and there is a white board/ramp there on the floor to help her get up the stairs smoothly.
Immediately after Finch asks Rosemary to call him Ponty, Smitty, who,was not present at the conversation, calls him Ponty. She could not have known his nickname.
When Finch picks up a copy of the How To Succeed book at the newsstand, he leaves without paying for it.
When all the secretaries are "working", they first change shoes from white to colored. After they make up their hair and stuff, a man yells "coffee break!" When they all get up to go, they're still wearing their white shoes.
When Finch is showing his advertising campaign to the directors, J.B Biggley says, "Bravo, J.B, you've done it again!" to Finch, using his own name.