This is tangential to your question but may come in handy if you run into any issues in BRU. You can try using the most significant carrier rule (see IATA resolution 302), which would either put it under KL's policy (marketing carrier), or if they waive it off to the operating carrier then you'll get the 1PC on that segment anyway.

As a word of warning, though...We did BRU-AMS-LHR/LGW-MCO back in late 2019 with the first two flights on KL and the long haul on VS in PE. The PE on the long haul should've given us 2PC each for the full itinerary but the staff acting on behalf of KL in BRU refused to honour that. We had 2 full suitcases and an empty one to fill up in FL, and they made us pay €60 to take an empty suitcase from BRU to LHR. They were essentially a bunch of dimwits who had never even heard of VS, let alone the joint venture. To add to the confusion all of this was ticketed and marketed by DL so under DOT Regulation 399.87 DL's policy applied, which clearly stated that the PE allowance would apply to all three legs. Even if they didn't know that then they should've applied the most signifcant carrier rule. But the staff had never heard of either of those (MSC or DOT) and threatened to close the check in until we paid. In hindsight, I should've taken an upgrade offer for the flight, which was less than the €60 and would've given us the extra allowance anyway.