Wall construction exterior wall KfW 40 Wall thickness 49

Because it would be the exterior wall construction 17.5 cm aerated concrete, 10 cm and 8 cm insulation, 2 cm air gap, and 11.5 cm clinker, but then we would end up with 51 cm, and the architect said that it doesn’t fit because he has 49 in the drawing. He said we would then have to make the entire floor plan's exterior wall 51 cm

If the wall construction you mentioned is built, the wall will be 51 cm thick in the end. That is correct because your list is missing the interior plaster. That is completely normal and is the case with all building plans as well. I just don’t understand the whole context now. The architect draws (as always with structural dimensions), so why is he having problems? It is always drawn with structural dimensions. Is he really a qualified architect?

Even if it is perfectly represented in the plan, you will be surprised in the actual shell construction that it does not fit to the centimeter.