Is a Gemarkung part of the adress when you have an actual adress like the streetname? Since Schmiechen is a part of the town Schelklingen and Müllergasse being a street might be the next smaller part of the adress I could not imagine that this is the position for the Gemarkung. But I couldn’t figure out what might be between street and part of town. So I searched Spitzacker around Schelklingen and found a page stating it is a “Weiler”. A Weiler is smaller than a Village, usually just a few buildings next to each other and without an own Administration. My guess would be, that osm mentions Spitzacker, because there was said Weiler and as Schmiechen grew it just became a part of Schmiechen. So while there is no actual Spitzacker anymore osm still refers to the historical area because the building might still stand. As of what part of the adress this might be: I don’t think it is a part of the adress. I think osm takes its information from the local cadastral office and they provided all informations including historic areas. The cadastral office is also your goto adress to get docs about areas. In german its called Katasteramt and should be in Schelklingen.