Basement insulation with different insulation thicknesses

Hello,

quick question... my basement was insulated with xps 120 mm. The general contractor probably miscalculated and ran out of insulation boards. Now the last top layer of insulation is missing. Yesterday a new delivery of insulation boards for the basement arrived.

However, from a different manufacturer and only 100 mm insulation...

He can't install two different insulation thicknesses on one wall, can he? I'm just a layperson, but that seems very strange to me...

Please help.

He can’t process two different insulation thicknesses on one wall, or can he?

With what insulation values? 100mm insulation can insulate better than 120mm. How is the transition from wide to narrow implemented?

Thermal conductivities are identical at 0.037

Is the specification sufficient?

I don't know how he wants to design the transitions, I just want to know first if that is basically possible and what needs to be considered.