They might not buy all of them. The military usually reserves themselves a right to buy hundreds of jets, but due to various conditions (such as a recession or the cold war ending) they sometimes don't buy all of them. There were some plans for 132 B-2 Spirit planes, but only 21 were made in the end. One of them crashed and was destroyed, and I'm not sure about the one that went of the runway last year, so there might only be 19 usable airframes at this point. You can't use all of them at the same time due to maintenance, so it could take months for all of them to get a chance to drop bombs from the start of an actual war. For the F-22 Raptor as well, an original idea in the 1980s was to order up to 750 aircraft, but only 187 production models were actually made. Not all could be made operational due to crashes and other damage.