A five numeral/digit serial number beginning with 20,200 plus the LW suffix is from 1953. The Cobra serial number range for 1953 was from 20200 LW - 26149 LW.
I don't know if I'd describe the finish on the grip backstrap as rough but it is quite textured and contrasts against standard bluing. It was advertised as making the guns more glare proof but it was primarily done as a labor and cost saving measure. It would only have to have been done along the top of the barrel, front sight, and rear sight plane on top of the frame if it had been done to reduce sighting glare. Areas that were left matte were the frame top strap, front grip strap, back grip strap, front of the frame under the barrel, the outside of the trigger guard and the cylinder flutes. These areas weren't polished as highly as the rest of the revolver's finish. This gave those rougher polished surfaces a matte contrast to the standard more highly polished frame and barrel surfaces. Colt called this treatment Dual Tone. All Colt revolvers from 1947-1954 had this treatment. This includes guns that were blue and nickel, all steel, or with aluminum frames. They all came with plastic grips Colt called Coltwood.
Starting in 1955, Colt reverted back to walnut checkered stocks with silver colored Colt medallions (excepting the gold medalliions of the newly introduced Python model) and all guns starting in 1955 had a uniform blue or nickel finish with no matte areas.
Just so you know, Dfariswheel is a founding member and a well respected Colt Forum member. He's one of the gents that taught me. I think he misread the serial number you provided. He has forgotten more about Colts than I will ever know.
If I misread it, I apologize.
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