When Joe Farnetti is describing California to Sam, he says that "even Lassie has a large car". While released as a novel in 1940, the first Lassie movie was not made until 1943, the year after this episode was set.
Character Joe Farnetti is asked if he has spoken to his parents. He says, "They give us six minutes a week." There was no phone service available between the USA and England until after WWII. (His parents are in California.)
The drug used to save Sam is streptomycin, referred to as a brand new, scarcely available treatment. Streptomycin wasn't actually discovered until October 1943, over a year later than the date given for the events in this episode. It wasn't used medically until after the war. The only drug available in 1942 to treat anthrax was penicillin, and there were only a handful of doses in the world at that time.
The action takes place August, 1942. The medicine that saved Sam, Streptomycin, wasn't isolated at Rutgers University by a graduate student, Albert Schatz, until October 19, 1943. Clinical trials didn't take place till 1946-1947.
The first time the murder scene is shown, Thomas Jenkins, right before he is stabbed, says, "Well, well, well so you turned up. Now this is a surprise." When the murder scene is repeated later in the episode, he says only, "You?"
The narrative refers to the historical sinking of the SS "Navarino", part of the ill-fated arctic convoy PQ17, on July 5th, 1942. In flashbacks, the (fictional) survivors Tom Jenkins and Leonard Cartwright are shown fighting for their lives clinging to wreckage in heavy seas, at night, with a thunderstorm in the background. In fact, July 5th is close to midsummer, so above the Arctic Circle, there would be light for twenty-four hours of the day; even at midnight, there would at least be a half light. Historical records show that the weather at the time was nearly calm, with occasional overcast. (There may even have been mirages caused by atmospheric inversion.)