XAUSA:

Years ago I ran a shop where we were jobbers for Browning, and that 90% bit has me scratching my head.

90% of Superposed guns maybe?

IIRC, some models of guns were not built with salt wood stocks at all. Wasn't salt wood restricted to Superposed guns?

Also, I seem to remember that Browning had salt wood information on an old website, but a quick check shows nothing. I bet a direct contact would get the whole scoop.