Which airline is responsible for delayed/lost luggage on a multi-leg journey?
A few days ago I was supposed to be flying PIT-YYZ-FRA-LED (first leg on AC, the rest with LH) on LH-issued ticket. AC's PIT-YYZ flight was overbooked. I voluntarily gave up my seat on that flight (couldn't say NO to 400 USD in cash) and was rerouted. My new itinerary was PIT-IAD-FRA-LED. First two legs were on UA, last one - on LH. The gate agent (working for UA, because United handles all AC's operations in PIT) managed to generate a new, UA-specific PNR-code for my itinerary and re-labeled both bags with the new tags, showing the new routing. Original AC's tags have been removed.
When I arrived to LED, one of my bags showed up but the other one was missing. I filed "property irregularity report" with the airport baggage handling agent and, since LH fly the last leg, received LH-specific file number. It has been almost 48 hours since then but the bag hasn't showed up in the tracing system.
If my luggage gets lost, with which airline shall I file the claim for compensation? Should it be LH (they issued the ticket as well as claim number), AC (their flight was overbooked, which caused my re-routing) or UA (they issued the bag tag)? Most likely the bag was lost by either LH or UA and AC has nothing to do with it. So, what prevails: UA's bag tag or LH's ticket and/or file number?
If the bag shows up a few days later, with which airline shall I file the claim for reimbursement for purchasing the necessities (toiletries, clothing, etc): LH or UA? And, if the bag never shows up, will I be compensated only for its contents or for the purchased necessities as well?