You can already see from a distance that the window reveal looks cleaner. As mentioned on the other side, maybe some fuss should have been made during installation, but appointments and time, I know—it's always easier to talk about afterwards. Still sad to see again, exceptions prove the rule and despite many good results, disputes keep happening.
Would it be possible, for example, to inspect the cellar elements at Glatthar’s factory, to get an idea of the walls, etc.? That would also be a point to possibly discuss topics in advance. May I ask which system you chose? Double-shell and filled on site with cast concrete? Are the walls really as sold, "smooth like plastered"? Possibly also the price per m²? Of course, feel free to send it via PM.
You have described it perfectly again. I now see that the prefabricated cellars are even tighter due to the double-shell variant and the cast on-site version, element by element. But as you said, the "white tank" needs to be interpreted differently.
From a soil report, it should be clear to the manufacturer which variant (DIN) is required for a cellar in the intended area, right?