What I can say is baggage claim is similar to EC261 compensation - airlines will try to avoid paying them as much as possible.

But bottom line - when you get serious, they will eventually pay you.

I took the liberty to look at SQ's CoC. SQ does list the common problems as excluded. However, the problem is there is no domestic flight in Singapore. So basically all flights are under Montreal. Because Montreal did not specify such exclusion, any exclusion, per DOT's interpretation, is a contravention of the purpose of Montreal.

So here you have it - they are liable. It is a question if you can push them enough to make them pay.