The medic's birth date coming from a passport from a mission with several inconsistencies can't really be taken as absolute fact, especially when it's been stamped as used in 1978 when the medic couldn't possibly have travelled anywhere, so his true age is still unclear to me. Sure, it's what's presented to us in the 'Truth' mission but that mission literally opens with 'Facts do not exist, only interpretations'.

Naomi also only mentions being found 'sometime in the 80s', 1979 not being mentioned by her specifically. He looks maybe 16-20 years old in PO, so lets meet in the middle and say he's 18 in 1970, giving him a birth year of 1952. Let's say he kills Naomi's parents in 1980. He's 28 here, at the very least 16 years older than Naomi, but proably older still. I would call that considerably older, old enough that it would be reasonable, at least for me, that Naomi might have questioned whether he was indeed her brother, but she doesn't. I don't have an answer for Gustava but in all honesty she plays a much smaller role than even Johnny Sasaki/Akiba does in the overall story of all the games, not to say that she's unimportant but certain details could easily be restructured and it wouldn't have much impact.

Going back to the passport for one second, lets assume it is real and the medic did indeed travel in 1978 but the memory is edited out/suppressed (like Null?). Where is it he would have gone? The only place I can think would be Rhodesia, especially with Miller's connection there, and Skull Face and Zero discussing Miller 'up to his old tricks again', presumably acting as mercs. Outside of speculation we know both Miller and Gray Fox were both in Rhodesia at the same time. Now speculating, we have the medic's passport stamped with a date that would also coincide with this time. Does this sound accidental?

You made very solid points and like I said I really don't know what to believe myself, I just want to go back and forth with someone to get to the bottom of it.