You never know whether the items were taken off the plane in SIN (cleaners, crew, other pax)... or continued their journey on the next flight.

I used to fly BA quite a few times but only on the SYD-SIN part of the SYD-SIN-LHR route, so my family and I always disembarked in Singapore. On our last trip we were booked into premium economy but had the luck of being upgraded to Club Class during check-in. Bonus. To cut a long story short, we left the plane in SIN with almost all our belongings... except for the kids' iPads which were hidden in one of the compartments and completely forgotten about.

We never got them back, but they did end up going all the way to the UK (location info). I'm surprised the cleaning services in SIN didn't find them, especially since this is Club Class we're talking about so I'd expect the seats to be perfectly prepared for passengers boarding the SIN-LHR flight.