The main difference is that the hammer and the thumb lever to break it open are reversed. On the 37, the hammer was rear and the thumb lever was farther forward. the 37a is reversed. the 37a also had a gold colored trigger.
Your Winchester model 37a was a reintroduction of the model 37 which occured between 1973-1981.That is when your model 37a was made.
A 20 guage WInchester 37A youth model will go for between $100-150 USD depending on condition.
These inexpensive Winchester shotguns are selling for between 55-140 dollars.
there are several listed at gunbroker.com
Serial # C861323
The winchester model 37-A was a reintroduction of the model 37 shotgun.these were made between the years 1973-1981.Winchester did not keep serial number records of the model 37-A. I am sorry but that is the best that I can do.
The 37A was manufactured from the mid 1960's to the late 1970's.
I have had several of the 410 37a youth and full value is 125 to 200 depending on condition
can you tell the age of a model 37a 20 gage Winchester by looking at the serial number
your winchester model 37 value is currently between 150-375 dollars depending on the overall condition and having between 60%-90% original finish and a good bore.
Between 90-200 dollars,depending on the overall condition of your shotgun and a good bore.
You will have to check the auction sites to see what they are currently bringing.