I like the 1-17 because it can help people learn the game with positioning. I think a replacement player like in the example you gave should have a different number, so it can be seen that, say, Sexton missed the game & Tia played. People who aren't so familiar with the game might think that Sexton had a great game whereas it was really Tia.
I am doing some rugby league research & quite often a player would pull out before a game another player would come into the team & wear the same jersey number. Unless you know what players look like, it can be difficult to find out who actually played. Fortunately, these days we have RL project to help us. The NRL's website is not as accurate as you would hope for these types of things. Also, most things are put up digitally now & get taken down or deleted soon after, so looking at this in the future causes problems.