Winchester 21 16 gauge clarification
 

I bought this model 21 16 2 barrel set along with a 20 gauge a while back. There is not a letter with this one. The forearm wood was not numbered or checkered the same as the rest of the gun. The 28" barrels are serial numbered to the gun but not marked DELUXE. The 26" barrels are marked deluxe. Since there is no letter I am asking for opinions on this gun.

You should get a letter. Don't worry about the second set of barrels not having a DELUXE stamp. Most Deluxe guns do not have a grade stamp on the barrel flats. Deluxe Grade guns were a very short era of manufacture and standard practices are hit and miss.

S in last picture
 

Does the S in the last picture of the barrels stand for skeet?

After sixty years of owning dozens of 21s, I have no idea.

The two DELUXE Grades I've saved pictures of have it as one word.

This picture was described as a De Luxe Duck with non factory engraving. This gun is close in serial number to the 16 above at 168xx. This production of 1947 shows the two word De Luxe. There is no letter available for the 16 two barrel set. The guy I got this gun from purchased it in the early 1980's. He said there was not a letter. What would be the best way to find out if there could be a letter?

Tom, try this...
https://paulinemuerrle.com/
Everything about 21's

Send your money to Cody. If there is no information, they will refund your money.

Letter
 

If you call them at 307-587-4771 they will tell you if a letter is available on that gun. But, from what I'm seeing it looks after market in the way the word is written.

All three Winchester catalogs I have that show it write it Model 21 DeLuxe in some places and DELUXE in others and toward the bottom of page 40 of the 1946 catalog they use DE LUXE. So absolutely no consistency between catalogs and guns. The catalogs picture the regular frame gun with checkered stock cheeks. The stocks of the extra cost special rounded frame guns don't have cheeks.