I've always wanted to know how these numbers are assigned to depth players and callups. Because they're kind of random but not all that random because there's a lot of recycling of 71s, 47s, 55s. Is the equipment manager the one choosing them and he just has a soft spot for certain numbers, or is it a thing where they say certain numbers are more legible to broadcasters and fans, etc. The latter is my theory since confusable round numbers like 89s and 65s haven't been seen in fifteen years.
If it were up to me and I were a callup I'd rather be the first #96 or #85 in Bruins team history than just another #71 or #43. Though I also can see from the management perspective that if you're just some part time replacement, you have to earn the honor of a unique number and by reassigning the same numbers you break them down like army recruits and get them in team-first mode (Lou Lamoriello famously took this to the extreme in NJ).
In the end I suppose it's a little of all of the above as to how they get these numbers.