I disagree totally with the resprayed hand idea. I've seen enough ratty old ones and am a firm believer that they were no more than mistakes. They seemed to proliferate in the late 1960s and can even be found on the small 24-hour hands from the gilt era.
As far as being resprayed, of course that is being done too. As far as radial dial GMTs having a genuine all red hand, it's nothing more than a compilation of parts to enhance the value of the watch. Way too late for the all red hands. Additionally, besides the all red hand added to the radial dial era, you'll also find many with the "blueberry" insert.