"credit only" attribute and cast order?

A few clarification questions: I came across with the TV series that in season 3 introduces a new opening credit sequence (in every episode). Basically in S3, all the "known" actors of the series are listed/credited, but not all of them appear in every episode (and before you ask: this is confirmed, I know all the actors, watched every episode, know this series inside out etc). So:

1) I should still list all the actors from the opening credits, but add "credit only" attribute to the names where needed (this roughly means 2-4 "credit only" names in every episode)?

2) How about the cast order? Should I still "keep" the cast order from the opening credits, even when some of the names are "credit only"? This would mean that e.g. numbers 1, 2, 4 and 7 are normal, but 3, 5 and 6 have "credit only" attributes.

Thanks.