What is significant about the letter Whit reads from the Western magazine ?

The man who wrote the letter in question used to work at the ranch.

Whit said, "Go on. Read the name at the bottom."

Slim read, "’Yours for success, William Tenner.’" He glanced up at Whit again. "What you want me to read that for?"

Whit closed the magazine impressively. "Don’t you remember Bill Tenner? Worked here about three months ago?"