Yea, after reading what you and OldUser said, and researching more, I think we're going to roll the dice and apply. And its what my father wants to do, he says while he still has the mental capacity to do so (he has health issues that are starting to affect cognition) And one lawyer says we should try . He is eligible with the grey area of continuous residence and proving continuous residency. Because they are vague on what counts as satisfactory evidence like Olduser has said, it can go either way- just depends on how well you argue or present your case. My mother is a US citizen for over 20 yrs, so my father could use the 3 yr marriage rule where his trips have lasted less than 6 months each of those years, however even though they've been married 46 yrs, in the last three years they have moved in with me due to health issues, and therefore have no joint bills, no joint accounts or joint lease, or joint taxes etc that are required for marriage based citizenship so between the two we think maybe 5 year provision would be "easier" Anyway, I appreciate the responses and will update here on the outcome.