There is no overlap between the two, except, say, that the Selected Alpine describes a route on Mt Edith and the Scrambles Guide describes the climb's descent route on Mt Edith as an ascent route.
But there is an overlap in that some of the easy "climbs" in the Selected Alpine, like the East Ridge of Mt Edith Cavell or the North Ridge on Mt Assiniboine, are mostly scrambling even if typically/historically done roped, and the "very difficult" scrambles in the Scrambles guide are pretty much of the same technical difficulty but on peaks that are usually/historically done unroped.
The classic route on Mt Lorette is one that might be in both, I can't remember.