The two sentences quoted were referring to the early days of the line. The Shays were originally used on the pass but were retired when the articulateds (rod engines) arrived. The articulateds operated over the entire line, though usually from Mack north over the pass to Wendella. #20 and #21 (0-6-2T rod engines) were also used on the entire line and went over the pass daily.
The NG Mike (#30) was moved over the pass using tender trucks in place of it’s leading and trailing trucks and used from Wendella on north for the remainder of it’s life. It was never used on top of the pass.