I had one RGN-KUL-SIN-LHR-JFK-YYZ-YUL plated by SQ. LHR-JFK on IB code share operated by BA.

The IB/BA segment was missing and canceled by IB/BA a long time ago. DOT refused to enforce.

Then there was the MH schedule change. TL.ca rebooked us on a later MH flight. They managed to issue a set of MH plated tickets attached to the original SQ tickets. On these MH tickets, there was the rebooked MH flight AND the IB/BA originally booked flight. So the BA flight was reinstated. Since then, I could see the flight on BA and IB websites.

So I thought it was good to go. But about 6 days from the IB/BA flight date, the segment was dropped again. I booked an AC B fare with confirmed upgrade on LHR-YYZ as an insurance.

The night before the BA flight, I got an email from MH. The email told me that the IB/BA flight has been reinstated but we were put on WL because the flight was overbooked. I checked, the next 3 BA flights out of LHR were showing J0 as well. So we probably would have to be stuck at LHR waiting for our flight to JFK and waste a whole day of our lives.

We are not the kind that would hang around and beg for 2 seats. So we decided to go to the city and had a bit of fun before heading back to the airport for our afternoon AC flight, and no-showed the BA flight. Another main reason for doing this is that we did not want to go home via the US.

So, to answer why fly's question. Yes. This is true. When we checked in at SIN, they still let us check in although the IB/BA segment was missing.