^^Yeah, sorry about the eyes.
Very few name actors hav EVER not taken billing on Trek.
Whoopi Goldberg--not because she was ashamed, but I think her $ rate would have been hign if she took billing, so she went unbilled and they paid her a nominal fee.
Judson Scott as was stated, because his agent was inept.
Madge Sinclair in "Voyage Home" don't know why--surely she didn't think Trek 4 was 'beneath her'
Rene' Aberjonois in Trek 6, because his part was originally cut and then when they restored it, they didn't change the credits.