"Does anyone know when they stopped using the four digit phone numbers in Las Vegas?"

Not exactly, but in the 1952 phone book there were 3 digit numbers, 4 digit numbers, and 4 digits followed by a letter. The Thunderbird was 5100.

In the 1955 book the Las Vegas numbers were all DU followed by 5 digits. (We don't have "53 or "54 books.)

You found some great matchbooks! I love the features, someday I hope we can find the Thunderbird and that El Rancho Vegas at reasonable prices....