Around 49 minutes, West shoots a hole in the key plate to open a door. Moments later (from inside view), as he bursts through the door, that same key plate is undamaged.
While inside the fake casket, Dr. Loveless is drinking cognac from a glass. This cognac would have spilled when his henchmen laid the casket flat.
An automobile can be seen passing by behind Pearline, the maid, at around 22 minutes in.
When West and Gordon infiltrate the Territorial Communications center, there is a sign that says "First Aid Department". The earliest use of the term 'First Aid' was 1878 in Britain.
The music the piano player is playing is the chorus from "I Left My Love", written by Stan Jones for the 1959 film THE HORSE SOLDIERS.
In the pre-title opening sequence, a brawl takes place in which the front zipper of Robert Conrad's britches becomes undone and remains so in the first shot after he's knocked out. The first practical zipper wasn't patented until 1891.
At 00:22:24, while "Pearl Hastings" (Grace Gaynor) has the drop on "Artemus Gordon" (Ross Martin), a car can be seen through the foliage, emerging from behind the white towel and travelling to the right. The street appears to be quite busy, as more cars speed by in both directions.