Is a number more likely if it hasn't occurred in a long time? Yes and no. In any particular game, no, since what happens in any one game is totally independent of what has happened previously. However, over a very long period of time, we can reasonably expect that the actual frequency of occurrence of any number will come pretty close to its mathematical probability. Therefore, if a number has occurred less frequently than expected over, say, a five year period, we can reasonably expect that it will occur more frequently than expected over an extended period at some point, so that the total occurrence will approach probability. There's no way of knowing just when that extended period will be, though. I suppose it's fair to say that the 631 trifecta is due if it hasn't hit in the last 1000 games.....but that doesn't mean it's any more likely to hit tonight than on any other night.
