I've never had a shorted box, but I come across tight, 'bank wrapped rolls' of mint state cents (same date, same mint), with two or three older cents mixed in, more often than one would expect.
Last year--for sampling purposes--I opened 20 Loomis cent rolls from my stash which appeared to be filled with solid mint state coins--same year and mint. Six of the rolls had a small scattering of old cents, the other rolls were solid. Had a similar experience a few years ago with Loomis and other 'bank wrapped rolls'.