Greg, when it comes to boxlocks, it's highly unlikely that William Evans was a "maker" at all. They did market well-made boxlocks, but the guns were made "in the trade" for them, by others. And you might end up paying more for the Evans name and London address than you would for, say, a Scott of equal quality and condition.
It's great to know exactly who made your gun, and when. But with a lot of very solid British boxlocks, that's impossible. I feel really fortunate to have a pair of Army & Navy doubles, Scott-made guns, in the original case which bears the original owner's initials. And, because the A&N records are available, I know both when they were made and the name of the original owner--who happened to be sufficiently famous (a British general) so I could learn more about him as well. But that's a pretty unusual case.
More often, you buy a gun about which you may be able to glean some basic information (like who made it and approximately when), and that's about it.
