Originally Posted by Madison Guy

I'm an AA flyer, not UA, nit I didn't think it possible to have both SSSS and Precheck on the same boarding pass. Indeed, that field enbedded in the PDF-417 code is a single character. Last I saw, it had four possible values: Reg, SSSS, Pre-check and even a value for No-Fly. But that was a couple of years ago. (Of course, I've had SSSS on an INTL return, and that carries forward to all connecting BPs - but with AA I was always able to have the BPs reprinted on arrival in the US for my connecting flights with Precheck back in INSTEAD of SSSS.)
Or, perhaps you are saying an agent manually wrote SSSS on your BP that was printed PreCheck?