Depending on the seller of the snake, you could have a hybrid. Something to keep in mind.
Otherwise, it looks as if the ventral scale count is the most divergent diagnostic feature of the two species --
L. ruthveni is 182-196, while the former
L.t. annulata is 42-56.
Sources:
http://www.kingsnake.com/king/ruthveni/ruthveni.html
http://www.kingsnake.com/king/triangulum/annulata.html
How to count:
http://www.arod.com.au/arod/scale/