GetRepetition ( RepeatingField ; Count ( RepeatingField ) - 1 )
Note that this assumes there are no empty repetitions before the last non-empty one.
I've read all the issues with repeating fields. But, what's done is done
It's never done - and it's actually quite easy to convert repeating fields to individual related records.
Aaaahh... that is the goodness I was waiting for. This works! Where I was going wrong was getting Last fileld, then -1.