Dick Hosmer wrote on Mar 9^th, 2012 at 3:08pm:

Such arms are not uncommon, and clearly genuine, though, AFAIK, the manufacturing authority paperwork has yet to be discovered. If anyone can dig it out, Joe will.

I'm pretty sure I already have.  The problem is they didn't work that way.  Springfield was charged with making the repair parts and didn't need a specific document to alter/update the design.  So there won't be any document for updating the stocks to the new design - there will only be a report of the stocks fabricated.  With year and quantity of course.

1580 were made in FY1899.  Those are them.  They're for the 1896 carbines.  After that they're just lumped into carbine stocks.  They weren't always big on models like we are.  They're just "magazine carbines." 

I bought a carbine with one of those stocks specifically to get an example for the book.