What if, and hear me out on this, there are generic Gen 1 and 2 Synths that gained sentience and a personality of their own? Not even prototypes, like Nick and DiMA, just regular ones they sent out on a mission or something. Their adaptive A.I. got "corrupted" based on the data they received. Maybe one out of 100 or more have a defect in their systems that makes them "go wrong" according to the the Institute.
I just think it would be really neat. Maybe there are old patrols living in seclusion that defected because something felt... off about their mission.
All this because I'm imagining a deep voiced generic gen 2 Synth wearing a straw farmers hat leaning on a rake explaining how he's not a prototype. He's the result of a broken component causing his A.I. to readjust and make him sentient. His name's Andrew. He admires Nick Valentine for making it out there in the Wasteland despite their very different origins. Doesn't know who DiMA is, though. Probably would admire him more due to how much more similar they are, history wise. Mostly, he's just a guy, chewing on the end of a piece of razorgrain, tending to his tatoes.