Detonics conundrum

[micromontenegro]

This little pistol has me over my head. Everything I read says Professional Models are Mark VIs. But here it is: a Mark I marked Professional Model, right above the serial number. How come? As you can see, it is an early, four digit serial number. Any info will be greatly appreciated!

 

[RickB]

I believe that the Mk. IV was the blued equivalent of the Mk. VI? Does your gun have the Selector rear sight with interchangeable leaves for elevation adjustment?
Mk. IVs should have the slide flats polished, as with the Mk. VI, but if yours is matte overall, then it may have been refinished?