1) Credits counted and not counted.
2) Time compression, in the past some movies were sped up slightly to fit on 120min tapes, I believe some of the Superman movies are examples of this. Obviously 121 and 122 minute films wouldn't fit on a 120min tape.
3) One of the copies is NTSC format , the other PAL. PAL tapes were always 4% faster than the film as it is one frame a second faster. If you include rounding in the calculations then that would work with your two runtimes.
4) The box is just wrong, someone typed in the wrong movies runtime.