Is only part of the building permit enforceable? How long is the building permit valid?

With us, the building permit officially expires if the construction is halted for two years. However, the building authority was extremely accommodating (I don't even know exactly when the previous owner stopped the work). So it was no problem to announce the resumption, and everything was fine.

I can only agree, politely inquire, and then you have a good chance of being treated leniently.