It's legit question time again, and it seems to me this is something of a repeat of a discussion some time ago.

Has anybody got any idea when beaverboard began being manufactured, and when its production stopped? 

In a case I'm working on here in North Joisey, a basement stair enclosure which clearly postdates the original house (reportedly c.1915-20) was built into a corner of what had been the house's main entry hall, using odds and ends of framing and  "clad" with 3/16" or 1/4" beaverboard.  Original house construction used wood lath and plaster over rough-sawn 1 7/8" x 4" studs; a presumably early infill of a doorway (leading from the stair hall to the adjacent living room; this doorway is also perpendicular to and predates the beaverboard-clad partition) was done in wood lath and plaster, and fairly smooth 1 11/16" x 3 3/4" studs.  Part of a porch nearby was finished with metal lath and plaster, applied over tar paper after shingle siding was removed from sheathing.  Much later alterations elsewhere in the house were done using gypsum board.

Although similar to homasote, the beaverboard here is marginally harder than homasote, but nowhere close to Masonite; it also has a tan/brown color reminiscent of corrugated cardboard, and you can see the little flakes of sawdust or whatever other lumber byproducts were used to make it.

The purpose of this exercise is to determine when this basement stair enclosure was constructed, with the ultimate goal of determining when the house was converted from single family occupancy to 2 family.

Thanks.

Ralph