Robert Mitchum should be in the main cast list

I never actually watched The equalizer when it was shown late nights on utv.
I was more stuff like Hill street Blues. But When I heard that Robert Mitchum
had appeared in a twi parter, I had to see that. Well I wasn't disappointed. He was as cool as ever. In the show, he is credited as special guest star. Yet here he is defined as uncredited. Come on, imdb get your facts right.