When dealing with buses, 24 passenger buses are basically the cut off point for minibuses. Usually a minibuse constitutes 24 passengers plus driver depending up the luggage arrangement for a specific make or model. The various types of luggage areas can impact seating capacity. Another thing that can also reduce your 24 passenger bus to seat fewer people is the option of a wheel chair lift bus which are usually 1 or 2 tie down and also reduce passenger capacity for a minibus.
Many times you will find that buses originally meant to seat 24 now have only 22 passengers, 21 passengers, 20 passengers or perhaps less in a special circumstance usually due to the wheel chair lift. Likewise you may find that many minibuses get label as 25 passenger buses when in fact this is probably not the cost most times. In most cases what the owner or seller / manufacturer means is that the 25 seat is for the driver of the bus.