I will jump in and ask a "leading" question.
Is this possibly a Lard trigger? Think of an Elsie single trigger.
I am certain that Westley Richards used this trigger as well.
FWIW Dept-----I find it very unreasonable to find a single trigger of any design on a Belgian guild gun unless it is the result of a Journeyman's efforts to rise to Master. If this be the case, it is usual that no name would be on the piece.
The more I think on it, it pleases me to think that this gun was built by a Journeyman in the Francotte factory. If that be so, all the questions would be answered with sensible explanations.
It would have been carefully used by the makers family and if new barrels were needed, a piece of cake to get them from the factory.
Best,
John

Humble member of the League of Extraodinary Gentlemen (LEG). Joined 14 March, 2006. Member #1.