Over the years, I've had ADs ask about ordering linemen's numbers as only 29 are available. I've always stressed that you can have duplicate numbers BUT advise your coach that youi can't have both in the game at the same time.
I once had a game that turned into a rout. The winning team was subing wildy near the end to get everyone in. When the game ended, a

wide-eyed wing ran upto me and said:
"REF, I think they MIGHT have had two number 79's in the game at the same time

!"
I responded: " IF we miss a foul, that's one that is to miss
![Cool 8]](http://www.refstripes.com/forum/Smileys/classic/cool.gif)
"