That square back variety like on this Bernhard Merkel drilling has no special name. IMHO it is a apecial "design" by the individual stockmaker, who thought it more "up to date" then. Remember, all those stocks were handmade, carved from a wood blank with a drawknife. A "Bayrische Backe" = Bavarian cheekpiece is that almost rectangular type, with both square back and front, often with a distinct flare out at the front bottom corner. The stocks by Schweigert and Lwe (top) are "Bavarian", as both have a near corner at the lower edge before running up to the comb nose.