Both my wife and I are 1Ks.
The question is whether LH or UA rules 'should' apply here. If we were starting the itinerary with LH, I'm pretty sure LH rules (two bags, as noted above, at 50 pounds each) would apply unless LH's agent chose to designate UA as the most significant carrier.
But since we started the itinerary with UA, I believe United's rules should apply (three bags of 70 pounds).
BUT when we changed the itinerary, the reissued ticket listed Lufthansa's baggage limits, not United's. I don't think that's right and, indeed, the baggage calculator differs from the ticket.
But the rules don't always seem clear. Possibly changing the ticket changes how the DOT rules get applied? I don't see why but it might.