Hi Mr.Crouse.....welcome to TFF.
Hopkins & Allen purchased the Forehand Arms Co. in 1898 and continued to produce their line of firearms into the 1920's.
H&A made both hammer-type and hammerless boxlock and sidelock shotguns, with both steel and damascus barrels, and in several grades. However, if yours is a "Plain Jane" shotgun.....no fancy engraving or such, they all have about the same value, according to the Blue Book.
90% - $195
80% - $160
70% - $130
As for date of manufacture......I know of no resource for Serial # to date of manufacture for H&A guns. Sorry.