Badminton Strings

Illisha and Vaibhav are playing a badminton match, in a best of 3 sets format. The player who gets to $21$ points first wins a set. In case the score is $20-20$, the first player to achieve a lead of two points wins. After the match, you see the referee's scoresheet to find that he has not written the final score but rather a sequence of characters, the $i^{th}$ of which indicates who won the $