Must all building materials be available when creating the structural design?

Hello!

Our architect commissioned a structural engineer on our behalf for the structural design of our single-family house.
A Poroton T8 was always considered. We were even thinking about choosing a T7.
Now we have received the structural calculations... Everywhere it mentions T9. It has a higher bulk density and should therefore be somewhat more "load-bearing."
Do all the conditions of the house have to be present and clear in principle when the structural engineer prepares the calculations? Or is a small buffer taken into account? It does make a difference whether ventilation ducts are still installed in the intermediate ceilings, thermal building activation is realized, and underfloor heating is laid. All this will also have an impact on the structural calculations.

Thanks in advance

Well, the static calculations (and the verification static calculations) are part of the building permit and must be clear beforehand. Subsequently, statically load-bearing parts may not be changed by openings. The underfloor heating does not cause any trouble there. Of course, materials change, but not on static parts.