Michael,
You got me curious...

It's been a long time since I've actually read any of our gaming guides (Maybe the publishers thought "Gaming Guide" sounded less risky or less sinful than "Gambling Guide"??).

Anyway, I randomly selected some from our collection...

Golden Nugget, 1949
Las Vegas Club, no date
Pioneer Club 1948
The Westerner, 1954
Desert Inn, 1954
Harolds Club 1949, 1960 & 1964
Harrah's, 1955
Aladdin postcard w/"21/Blackjack" info, 1962 & 1968
ALL of them used the term standoff

Ran across an interesting tid-bit in the 1955 Harrah's guide...
"BLACKJACK Formerly any black Ace with a black Jack. Now the Blackjack feature of the game includes any Ace with 10, Jack, Queen or King; total 21, 2 cards."