Help identifying a Stevens 311A .410

I have a beautiful little Stevens 311A SXS in .410. I will be putting it up for auction on GB and I know very little about Model 311's and need some help to properly identify it.

There is no serial number, so it must have been made before 1968. The only identifying stamp, other than maker's name and Model 311A, is an oval with 188 in the center. It has 3" chambers.

Any help would be appreciated.

It appears to be a typical Model 311, with case colored receiver, 26", blued steel barrels and nice walnut stock and fore wood, etc.
I have searched the web for info and found that production of the 311 started around 1940. In 1949, Stevens stamped the bottom of the receiver with a circle and a letter inside the circle, starting with A for `949. The last letter I can find is the letter V = 1968.