When Monaca Grey is shot the TV news broadcast is just starting as the announcer reads the lead story. At the end, the broadcast is recreated with the exact script and timing. This would indicate that Monaca Grey is shot at 10 PM and takes 25 minutes to unplug the TV, not the 30 seconds as originally shown at the start of the story.
In the scene where Ellery tells his father that he knows who the murderer is, when looking at Ellery's face view he is wearing just a shirt, but when looking at his back he is wearing his brown jacket.
When Ellery picks up a photo of Monaca Grey after her murder it is a upper body photo with Monaca in a dark colored dress. When he puts the photo down, it is another woman, full body photo, sitting on a chair, in a white dress.
Ellery and his father are seen driving on a street for about a half a minute when Ellery goes through a red light. But when the wide angle of the intersection is shown, the street that they are on ends just one block behind the traffic light.
The smoking jacket found in Monica Grey's apartment is a medium. Carson Mckell is at least a large if not an extra large.
The wall socket from which Monaca Grey pulls TV and clock cords is a 3-prong grounded plug which were not standard in 1947. The 3-prong socket and plug became new construction code in 1962.
When Ellery and his father are driving, it shows the traffic light going directly from green to red. The modern three-color traffic light with yellow (amber) was standardized in the 1930s, so no lights in any major cities were still using only green and red by this time.
Ramon's address, 715 West 96th Street, would put his apartment building somewhere in the New Jersey side of the Hudson River. This isn't uncommon for television shows set in New York City, but an actual address is used for another building, the one the McKells and Monica Gray live in.