Ah, I think I know what is going on.
The supplement that gets displayed from the keyword will be from the option that is selected, not from the Correct answer option.
There is this note on the Details screen of the question assets:
|Note: Supplementary content related to a Question Option (specified above) can be provided in this section. This content is intended to provide further information related to a Question Option to be shown upon completion of the Quiz. This content can be printed in the “Thank You” bodycopy.|
If you enter supplement values for each option does something now appear on the Thank You page bodycopy on the front end?