I never really understood it.
They rounded up the Drugborn precogs — the ones who’d gotten the talent from a massive dose of K-459 — in days, mostly because they had no place to hide: you could tell them on sight from the skin discoloration, and from the eyes.
But with the second-generation precogs, the inheritors, there aren’t any physical tells. They could blend in, hide among the genpop, hide in plain sight. But they found ‘em.
Then I realized: they’ve got Drugborn talent-sniffers. They’ve got some formula that lets you feel or smell or see or hear the talent.