well, box set.. which films would you include? there's nothing like an "official series" really in terms of plot and so on, it's more like Sartana being a popular character like Django, which doesn't mean there's a continuing story or related content in story.
i know what you mean though, just like there's a Sabata box, but also: Yul Brynner is not Lee van Cleef, and his name is not Sabata, his name is Indio Black.
Just like there's a Django box in Germany, but Texas Adios is not Django, although it's called like that in Germany.
I think box sets are very problematic. I'd rather have a Garko box than a Sartana box, because that would evade the title problem