@coolbean --
Here's a link to a document from the Illinois State Bar Association. The link discusses the issue of how to prove non-residency in Illinois.
https://www.isba.org/sections/statelocaltax/newsletter/2010/06/imanonresidentofillinoismaybe#:~:text...
Personally, I think a copy of your part-year resident California tax return, including Schedule CA (540NR), might be helpful in proving your case, since it includes the date you became a California resident and it documents that you paid CA taxes from that date.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
