Why are there so many different versions of the Zapruder Film?

Does Frame 188, for instance, need 5 different versions?

Why are there so many versions of the Zapruder Film? And what is the reason for continuing secrecy after 60 years? The National Archives and the Sixth Floor Museum in Dallas claim that the copyright over the film prevents FOIA requestors from obtaining copies of Zapruder Frames, even those behind the poor black and white copies that were published by the government in the 1964 Warren Report Volumes. (See Above) It makes little sense that the public is not allowed to inspect copies of the slides that were published by the government 60 years ago. That the photos were originally published in in such low quality black and white is reason enough to want to see the original color photos.