This covers a whole variety of little things that have happened, so bare with me.
1. OK, a small one. If I'm not mistaken, on more than one occasion when someone on the ship experiences time travel Chakotay is seen, am I correct? Anyway, in the first two seasons above Chakotay's left temple there is a small patch of gray, but when someone goes back in time, its no longer there. Did Chakotay dye his hair in the first season?
2. The Janeway hair problem. Now, usually when there is an "old" episode, that took place during their first two years in the Delta Quadrant, Janeway has her hair in a bun, with the exception when her and Chakotay are left behind. Anyway, in one incidence, in the episode where we meet up with the 29th century ship that is Voyager's "guardian angel", Janeway has to go back to prevent Captain Braxton from destroying the ship, she does not wear the bun and no one questions the sudden hair change.
3. --A more recent boo-boo. In the most recent new episode with the Klingons, there is a small mistake. If you will picture the movie The Undiscovered Country, the Klingons are wearing semi-different attire than the ones in the Voyager episode. The attire isn't the current, if I'm not mistaken, but it is most likely a mistake. Also, in The Undiscovered Country, the cranial ridges on the Klingons are less pronounced than the ones in the Voyager episode.
That is all for now, there may be future updates.
Either a knowledge of the series or the whole series on tape.