On a slightly related point:

Later this month, I'm scheduled to fly QR (EWR-GVA), connecting to BA (GVA-LHR), on separate tickets.

When I phoned QR, they told me that they would through-check my bags onto the BA flight (thus allowing me to use my 2pc allowance all the way to London).

However, I read in this thread that QR wasn't so willing to interline onto a separately-booked flight on SQ (with whom, they apparently also have an interline agreement).

Is this really so discretionary? Was I misinformed by QR reservations?