The policy is that you won't be able to short check or collect a bag. If you have a copy of your fare rules, which of course you "agreed" to, you will usually find text buried in there confirming this policy.

• Up to 24hrs transit - bags are checked Through
• Over 24hrs transit - not considered a transit, you collect bags.

The reason for this is to help prevent hidden city ticketing and hence revenue loss. Basically when you have a connection >24hrs it's considered two separate flights and different taxes and rules apply.

You might be able to persuade check-in at SIN to give you an exception for one/both bags but you should not expect it and I wouldn't push too hard.

If you really need to pursue this and you get pushback, ask the check-in agent to call their supervisor and ask if they can make an exception - the front-line staff are outsourced but the supervisor is usually a direct QR employee and may have some scope to bend the rules. It's probably best to try to do at main check-in and not at the courtesy early check-in desks in the Jewel as you're unlikely to have the QR employee/supervisor there.

It would be better for you to plan to have whatever you need in Qatar squirreled away on your hand baggage.
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Good luck