Another clue to the code

The Christmas gift code:  0, 8, 18 or 19, 20, 22.

Clue for today:  If a certain 17 year old had kept a specific appointment on Monday, her number would be changed to be 4 more than her original number.  So if you can figure out the reason behind the code ... now figure out who belongs to which number!

Now that would have been fun!  Can you just imagine ... a specific number crossed out with a new number written next to it!!!