The positions of Mrs. Robilotti's arms change between shots in her first scene.
While Mrs. Robliotti is yelling at Archie making accusations, the man at the piano stops her and warns her that what she is saying is libelous. There are two errors. Slander is the harming of a person's reputation by telling lies about the person. Libel is writing lies that harm the person's reputation. So, it would be slanderous not libelous, except the lies have to be told to a third party and actually cause harm, simply hollering at the person is not slander because no harm to the person's reputation occurred.
The series dress appears to be from the 30's and 40's, yet the vehicles on the set include a '58 caddy and other "late model" cars
The books chosen date from the 1930s to the 1960s. Rex Stout never aged the characters over the 30-40 years he wrote the books.
When Archie is talking to Mrs. Irwin, he says, "If she [Mrs. Robilotti] knew I were here trying to get support for my belief that Faith killed herself, I think she'd have a fit." But Archie believed that Faith was murdered, not that she killed herself.