In my experience when checking through bags from TG to LH, in 100 percent of cases (double-digits) I had to present my baggage tags to the LH gate agent so they could enter them into the system for my onward flight and request them to be loaded. The first time I did the checking through, I relied on the TG agent's word that my bag tag numbers would automatically get added to my ticket record at LH. The bags ended up not only not making it but Lufthansa in MUC initially refused to take control of the bags at FRA to fly them to MUC. It took the two agents at the lost bags desk plus a supervisor and a call to Frankfurt to sort this out.