Lots of tell-tale signs give evidence to certain periods of production.
Like: where is the barrel band? in front of or in back of the front sight?
What type of front sight? ramp and dovetail or post and blade, or?
Long ramp or short ramp or no ramp?
Sight hood or no sight hood?
Rifle or carbine?
Carbines have a barrel band a couple inches from the front end of the forestock, wrapping around the barrel, magazine tube, and stock.
Rifles have a metal cap at the front end of the forestock.
A 'short rifle' is carbine length with a metal end cap instead of the barrel band.
Curved buttstock, carbine buttstock, shotgun buttstock?
Saddle Ring, Northeastern, Eastern? They all have different characteristics on the same action. Just read about the 'Northeastern' today and the description fit mine; it came out of Eastern Maine in 1927.
And the beat goes on. It all has a bearing on age and value.
Look up the serial number or post it here and someone will tell you what year it was manufactured. There are several publications that carry that info; mine happens to be a well-worn magazine issue entitled "The Legacy of Leverguns", Rifle Magazine's special edition Winter 2000.
You might even find something online if you Google 'Winchester serial numbers'.
It's not really a big mystery, just a bit of research. Winchester is alive and well, at least on the WEB and then there is the Cody Museum, where, for a price, you can get a letter describing your rifle/carbine based on the serial number you provide to them. The letter will probably increase the value of your rifle/carbine more than the fee they will charge. Happy Hunting! It's just a 'click' away....
Regards,
Sweetwater