Your Winchester model 37a was a reintroduction of the model 37 which occured between 1973-1981.That is when your model 37a was made.
Blue Book of Gun Values
The 840 was a cheaper version of the Model 37A which in turn was a follow on from the Model 37. As far as I can tell the 37A was manufactured between 1973 and 1980. All single shot models were discontinued by 1980 so I would assume it is aged somewhere around the above dates.
1957
your Winchester model 12 pump shotgun was made in 1936.
My information suggests that you have a Winchester model 101 which was chambered in either 28 gauge or 410 gauge,which was made in August of 1970.
The model 37 was produced from 1936 until 1963. They were not serialized.
Was made 1936
Impossible to answer without the serial number.
The Winchester model 1400 MK-II was made from 1968-1972.
Your Model 12 was made in 1914, the 3rd year of production.
The Winchester model 120 ranger was a economy version of the Winchester model 1200 shotgun.the model 1200 was produced during 1964-1981,and the ranger was also produced during this time.