exceptional substitution question

[refinks]

I'm working with a newbie in a tri tonight, and I'm thumbing through the rulebook to make sure I don't sound like a complete buffoon if she wants to ask me some specific rules questions. I stopped when I came to the exceptional substitution part, because I'm wondering if I could have applied it to a situation in my JV tournament a couple weeks ago.

I'm going to try to recreate the situation the best I can. Team had 8 players, plus libero, so 9 total players in uniform. 2 players had already been subbed for and one of the players that had NOT been subbed for suffered an injury that caused her to miss the rest of the match. They had no legal subs. Coach was fairly new, asked what his options were. I thought about it and determined that an exceptional sub doesn't apply until you've used all 18 subs, so I told him that his only option was to pull the jersey off the libero and make her a regular player. He did so, and we played the rest of the match with no problems.

Now I see in the rulebook that an exceptional sub is permitted for an injured/ill player when the team has exhausted their 18 subs or when no legal substitutes are available. Now, the way I'm reading it, in my case, I could have told the coach he would be allowed to substitute for the injured player with one of the 2 subs that had already subbed for somebody else. Am i reading too much into this? For future reference, I'm just wanting to know the correct ruling on this. Thanks.