The OSL problem happens because at this station LH is handled by SK and when their DCS takes over it reassigns everything. Happened to me in ARN too. The good part is that thee row behind C is hard coded 'last off' and gives the gate/checkin agent the flexibility to assign you a new nice seat.

The problem described by the OP will get more tricky once LH switches to auto checkin everyone this year. Seats will be assigned whether the pax checked in or not and then a nice mess will appear. Already the issue with SK handled and operated flights.