The film loader cannot read the as yet undeveloped edge markings so there is no way for it to know where the numbering starts. Setting the ISO is just a reminder for yourself of what speed the film is that you have in the loader and usually people use the red and white dots to indicate B&W or colour film. The reset button is simply there so that you know how many frames you have wound into the cassette, so you should reset it each time you load. Everyone who bulk loads film has to live with random start numbers on their negs.