I don’t know when the 1873 stamping was stopped.  I am not sure when it started, either!  My 1985 edition of “The Winchester Book” covers Model 1873 carbine rear sights on pages 187-188.  He says the adjustable leaf sights (carbine rear sight was what the catalog called it) were usually marked 1873 on the upper portion of the leaf, but that a few were not marked.  Finally, he says the date is the year of introduction, not the model of the gun.  

I take exception to this last statement.  It doesn’t make sense.  The carbine leaf sight was different for 1873 and 1876 models.  Also, the original carbine rear sight for the 1873 was a simple non-adjustable leaf type.  The carbine leaf sight with adjustable slide first shows up in the April 1, 1882 catalog.

What is the serial number of your carbine?  

Here is a carbine leaf sight on an 1873 carbine, SN 156798.  No “1873” markings.

Here is a photo of a carbine leaf sight on a Model 1876.  Note that it is marked “1876.”