Just carrying on this discussion, though slightly different perspective.

Trying to book a flight that starts in a European city not fed by UA to another from which I will take a UA flight.

Options would be
1) LH flight, LH flight number (euro) then UA flight TATL (UA flight number)2) LH flight, LH flight number (euro) then UA flight TATL (LH codeshare flight number)
3) LH flight but UA codeshare flight number then UA flight TATL (UA flight number)
4) TK flight, TK flight number then UA flight TATL

Assuming cost differential is minimal which option offers best overall protection? The layover in Germany is about an hour.