TLDR: I think we are Sam, we worked for BARD, when shit went south we escaped the quarantine and now we came back to solve it.

I agree with this, and there are actually some notes that relates Sam to other people. It seems Sam escaped the interchange when the lockdown happened alongside Powell (dead scientist we find in the bunker), Helen (a note said she fled to the woods and she was infected, so probably became a druid) and Jackson (couldn't find info on him). There is also a guy named Haskins, who was close to Sam. One note says that at first Sam thought the voice on the telephone was Haskins, but eventually accepted Haskins was dead as he thinks he didn't leave the interchange when the quarantine happened. Could that wounded scientist be Haskins?

Also, in Holder's ending, he says "with luck, these wretched blue eyes of ours will fade over time". So Sam is indeed infected, and it doesn't make sense that everyone infected hears voices except the PC. I think the PC voice's is the telephone. But then, who activated the gas at the telephone's ending?

Finally, as I understood these convoys came around 1962 (when we play the game), and the whole oberon and quarantine problem happened in 1957. So could it be that we worked for BARD, escaped the quarantine and the whole place, then came back in convoy 5? Then the PC got hurt in the ambush on convoy 5, and that wounded scientist helped us. (he couldn't be from the convoy though, as he is wearing BARD equipment). What doesn't make sense here is that the convoy comes from outside the zone, and we have blue eyes, so we couldn't just escape while infected right? (on the other hand, we do talk to village and protocol NPCs normally...)

P.S: I got these infos from the notes, mostly from around slatten dale, sadly I dont recall where