Applescript Repeat Loop Not Returning Expected Results - applescript

Question

I am trying to "find-replace" a series of superscript cross-reference letters with numbers in Adobe InDesign. I have two "hard-coded" lists
set myLetters to {"a", "a", "a", "a", "a", "a", "a", "a", "a", "a", "a", "a", "a", "a", "a"}
set myNumbers to {"1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15"}
It seems fairly straightforward but the script changes all of the occurrences to "1" on the first iteration and thus all subsequent replaces are ignored because the find is "false"
Any help and insight would be very much appreciated.
Here is the script as written:
tell application "Adobe InDesign 2023"
set myDocument to document 1
set include footnotes of find change text options to false
set include hidden layers of find change text options to false
set include locked layers for find of find change text options to false
set include locked stories for find of find change text options to false
set include master pages of find change text options to false
set whole word of find change text options to false
set case sensitive of find change text options to true
set search backwards of find change text options to false
set find text preferences to nothing
set change text preferences to nothing
set mySelection to selection
tell myDocument
set myCharacterStyle to object reference of character style "sup" of character style group "Cross References"
end tell
set myLetters to {"a", "a", "a", "a", "a", "a", "a", "a", "a", "a", "a", "a", "a", "a", "a"}
set myNumbers to {"1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15"}
repeat with i from 1 to count of myLetters
set find what of find text preferences to item i of myLetters
set applied character style of find text preferences to myCharacterStyle
set change to of change text preferences to item i of myNumbers
change text mySelection
end repeat
end tell