I guess I don't understand where everybody gets the idea that every checked bag will be searched starting friday. An airline can choose to hand search every piece of checked baggage. If they choose the hand searching option then they do not need to do anything else and bag matching will not be done (indeed if every piece of checked baggage is searched the reason for bag matching goes away). Bag matching, though, is an alternative form of security screening of checked bags that does not involve xraying, sniffing, or searching every bag. It happens daily on every international flight and has for 10 years now. Plus even if a particular airline decided that they did not want to do bag matching and wanted to do xraying or handsearching instead, they are not looking for knives, box cutters, etc, they are looking for explosive devices as Doppy noted (hence the reason explosive sniffing dogs are an alternative).

If every bag loaded on the plane is not accompanied by a passenger who has gotten on the plane then the unaccompanied bag must be offloaded - this is how most delays due to bag matching will occur when someone does not board the plane after checking their bags(maybe because they are stuck trying to get through security?).

Xraying of checked baggage sometimes can lead to handsearching of that baggage. For example when the xray shows sometimes that looks like a bomb. Then the bag must be opened and checked. This is what occurs in some european cities.

Not trying to argue with you Cordelli but I just don't understand why people think that bag matching means hand searching of checked luggage.
jerry