Marvel Built? Yes? Or No?

Medical doctor buddy bought this gun for casual shooting.  Just put a hardball recoil spring in it for him so hopefully he would not kill it with 230 ball.  Bullseye gun built on Caspian slide and frame.  External extractor slide, Marvel rib,  Kart barrel, no marvel disconnector cut, standard grip safety tang.  The underside of the slide is marked with a 3 digit number that does not match the last three digits of the serial number.  Gun feels good.  Barrel locks up nice.  Slide to  frame is well done and slick.   Did Bob Marvel mark his work this way at any point in time?