Compiled exam packages would have to record the parameters used to compile them, such as the MathJax URL, and the LTI provider should send those with the request to fetch an updated package.
I think the reason for this is that we have custom MathJax URLs set on our user profiles on the Numbas editor, but when the LTI tool fetches a new version of the package it just uses the default URL.
Compiled exam packages would have to record the parameters used to compile them, such as the MathJax URL, and the LTI provider should send those with the request to fetch an updated package.