https://www.oneworld.com/airports-destinations/baggage-information/baggage-queries-during-travel/

I was intending to print out this page to show. I'm quite prepared to accept the economy allowance though I'd argue the MUC to LHR flight is a feeder flight. Equally I'm going via MUC to avoid 8 hrs getting bored in the Doha lounge and to save £400.

I think the interlining is quite clear with that policy. Doesn't state anything about being on the same itinerary or PNR but I accept that the airlines can make up the rules on the spot.