Lack of records and central government will make this very difficult. On top of the fact that most Railroad refugees (aside from Danse apparently) have plastic surgery to adjust their appearance. Random DNA sampling has a lotto winner's chance of revealing it, and I don't see the BOS being able to check everyone in an area.

Too much manpower too busy doing more important things.

Yeah but possible if it was the driving force that some claim it is, hell they could set up DNA testing in the Settlements while giving out free medical care......good PR and they can hunt Gen-3s at the same time.

But of course it isn't a priority, beyond ensuring no other Gen-3 have joined or attempt to join the Brotherhood.

I've noticed that it seems that the Brotherhood set their checkpoints up at Power Armor sites which would suggest a switch to tech retrieval......shame I've already acquired all the suits already. Does anybody know if the other winning factions set up in the same locations?

They do.

You'll note most of those sites are old US Army checkpoints as well. Seemed like every time I zoned into Greygarden in my first game, the one east of it was under attack and had reset its ammo boxes to full.

Well that makes it easier to collect power armor after the main story anyway.