Clearly, adding old dough to a new dough is not confined to white flours. I had a small bowl of excess Schrotbrot dough left, which went into a very basic rye dough. Final proof was in the fridge. Very moist and good.
Mix and knead 250g old dough and 300g new dough (110g rye flour (= 60%), 70g wheat flour (= 40%), 125g water (=70%), 2g fresh yeast (= 1%), 2 tbsp sugar beet syrup, 3 tbsp rolled oats, 4g sea salt (=2%)), prove for 1 hour, then shape, put into a tin and let rest in the fridge overnight. Baket at 220°C for one hour.