No anguish here, just attempting to get it right and explain why I think what I do.
As a Gibbs Farquharson and F.C. Selous fan, I'm a bit stymied as to why there are so few good photographs of the man.
One would think that his exploits with so many prominent people and his fame, there would be more photos and information on Selous.
One point that actually just came to me is that Selous is quite aged in that photgraph, well beyond the time that he got rid of his Gibbs and was using nitro rifles, from Holland and Holland and others.

Your comment on the Selous plated rifles is quite correct.
There are many (most) which F.C. Selous had no connection to. One reads on the net all sorts of claims about that. Even professional writers have claimed that every one was ordered or owned by Selous himself. My thought is that he must have had at least two made for himself and there are reports that he outfitted some of his staff with Gibbs Farquharsons as well but there is no information as to the configuration or the number of those rifles.
Of course, the advent of the internet has shaken the trees so to speak, so there are so many otherwise unknown firearms of all types coming to light as well as a better understanding of surviving numbers and variants.