The mantra from influential "experts" at the time hammerless guns were being developed was that all of them should have interceptors or tumbler blocks -- esp any hammerless gun pretending to be a "best" gun. For the first quarter century of their existence, boxlocks were able to give sidelocks a run for their money in the "best" category, and it followed that many of the highest quality versions were fitted with intercepting sears, whether they needed them mechanically or not. Diggory probably has a better handle on it, but I think they start disappearing from British boxlocks somewhere around 1900 and are mostly gone by the First World War, at least in the British trade. The Germans are a little different.