Flannigan and Moe use 1940s slang terms for money; a "fin" is five dollars, and a "sawbuck" is ten.
First appearance of recurring character Frank Flannigan.
Velie mentions a "new Mickey Spillane". He's talking about Spillane's first novel, I, the Jury, which was published in 1947.
Freeman mentions, in 1947, that superhero comics are on their way out. In reality, the four major comic book companies kept publishing superhero comics through the end of the 1940s and into the 1950s. DC Comics (then National Comics) canceled most of their superhero books in 1951, with only Superman, Wonder Woman, and Batman surviving the purge. Fawcett (which published the Shazam! comics) continued publishing them until 1953, as did Quality Comics. Marvel Comics (then Timely Comics) was the last to cancel their superhero comics, with the last being published in 1955--with DC Comics reviving the concept in 1956.
When Ellery is talking to Frank he says 'The Adventures of the Purloined Gun' not 'The Adventure of the Purloined Gun'. He uses the plural, not the singular.