Interesting.

Not too long ago, my wife -E50k- flew from BOS to LIS through YYZ and LHR, on two separate tickets, BOS-YYZ and then YYZ-LHR-LIS, both in J. Last leg on TP. (I joined her at LHR.)

The BOS AC people would not check her bag all the way to LIS; claimed they were unable to. They offered to either check to YYZ, or to LHR. Of course neither made sense since she would need to go through immigration to retrieve her bag and recheck it.

This was an issue even though the bag was carry on size, since she is more or less unable to lift her bag to put it in the overhead bin.

OTOH we did not need to wait at LIS.