Thanks for the replies.
I had thought that ancestry.com would actually provide an answer to this question (still hoping!) as they have attached it to their records and links as a "source". Usually sources are complied from historical links. I have been using some of the "millenium file" links as correct??
From your replies it seems this is not so. I must admit where dates did not match I just go with what I already have and use Familysearch as the reliable source.
I guess this must be the case especially as ancestry.com has not made any attempt to provide a definitive answer.
Would still like an official response from ancestry.com regarding the "millenium file" sources.