A bag that does not appear on the belt is far more often delayed than lost. The system that moves it records where it has been scanned, which is why most bags are located within a day.
Bags are tracked by scan events
Every checked bag carries a tag with a unique number, scanned at check-in, at sortation, at loading and at transfer points.
Each scan writes a record, so the bag's last known position is generally known even when its current position is not.
A bag that missed a connection therefore shows a scan at the transfer airport and no loading scan, which identifies the problem immediately.
Most delays happen at transfers
Connections are where a bag has the least time and the most handling, and a delayed inbound flight compresses that further.
Bags are loaded to a schedule tied to the departing aircraft, so one that arrives at the sortation area after the cut-off simply travels on the next service.
This is also why bags on separately ticketed journeys fail more often, since nobody is responsible for transferring them at all.
The report is what starts the process
Filing a report before leaving the airport creates a reference that links the traveller to the bag record and to a delivery address.
A description of the bag matters because tags occasionally detach, and unmatched bags are reunited by physical description rather than by number.
Delivery is arranged by contractors once the bag arrives, which is the stage that usually takes the longest rather than the locating.
Interim expenses are covered but bounded
Airlines are generally required to cover reasonable essential purchases while a bag is delayed, subject to their own policy and to international liability rules.
Receipts are required, and what counts as reasonable is interpreted narrowly, so replacing an entire wardrobe is unlikely to be reimbursed.
Travel insurance delay benefits often sit alongside this with their own waiting period, and both may apply to the same event.
Reducing the exposure
Carrying medication, documents, a change of clothes and anything valuable in the cabin removes most of the consequence of a delayed bag.
Removing old tags, labelling the interior and photographing the bag and its contents all make identification faster if the tag is lost.
Longer connections are the most effective single measure, since the bag needs the same time the passenger does and has less ability to hurry.