Recently bought in this Blanch hammergun for restoration. Nothing to write home about: a Scott manufactured gun for the trade but tidy none the less and with great barrels.
However one interesting feature is the top tang. This has been extended and an additional screw has been used. Judging by the engraving, this was done before original sale but to what end, we will never know.
Only likely explanation I can think of is that the stock had a shake or crack and strengthening was advisable.
And the Scott patent stamp: