When Owen gets depressed about MASH finishing, even though that was over a year ago, it may not be a mistake, but rather that, being out at sea most of the time, he might not have been able to watch it until it reran - or he was just a bit thick, and it took a while for the news to sink in. As for Roger mentioning Godfather Part III, this is not necessarily a reference to a movie that did not come out for another six years, but it is more like how people speak of World War Three, even though that has not happened yet, so it is as if he is saying that Corey's talking about the family was reminiscent about the first two Godfather films.