Since it's original publication in 1950 through the present, how has
"The Chronicles of Narnia: The Lion, The Witch and The Wardrobe"
ranked on Best Seller lists?

Remember it is not one book but seven small books and it is a kids book.

It is also a paperback and hardback and has bee a steady seller for many years.

Bestsellers are flash in the pan stuff.  There is a ton of it out there used.

In the best selling children's books of all time(paperback)
91. The Lion, the Witch and the Wardrobe by C.S. Lewis (Macmillan,
1970 and HarperCollins, 1994) 2,446,861 (figures not available before
1994)
203. The Magician's Nephew by C.S. Lewis (Macmillan, 1970 and
HarperCollins, 1994) 1,591,435 (figures not available before 1994)
340. The Horse and His Boy by C.S. Lewis (Macmillan, 1970 and
HarperCollins, 1994) 1,136,640 (figures not available before 1994)
362. Prince Caspian by C.S. Lewis (Macmillan, 1970 and HarperCollins,
1994) 1,061,954 (figures not available before 1994)
375. The Last Battle by C.S. Lewis (Macmillan, 1970 and HarperCollins,
1994) 1,004,296 (figures not available before 1994)
376. The Silver Chair by C.S. Lewis (Macmillan, 1970 and
HarperCollins, 1994) 1,001,907 (figures not available before 1994)

In the best-selling children's books of 2002:
36. The Lion, the Witch and the Wardrobe. C.S. Lewis, illus. by Cliff
Nielsen. HarperTrophy, 1994 (229,622)
42. The Chronicles of Narnia. C.S. Lewis, illus. by Cliff Nielsen.
HarperTrophy, 2001 (209,719)
73. The Magician's Nephew. C.S. Lewis, illus. by Cliff Nielsen.
HarperTrophy, 1994 (159,242)