I recently went through the use tax thing this for in and out of state purchases with the board of equalization. When they sent me a form/questionnaire, I returned it with a bunch of receipts, tax forms, and a check for what I owed (avionics only). I neglected to include the note I wrote to explain it all.
They sent me a bill more than doubling what I owed. After a phone call and talking to the person that had my paperwork, we were able to discuss what was purchased and when and where. I had purchased the kits over a 14 year period and mostly out of state. The finishing kit I did buy in CA, but paid the use tax already on my state tax returns.
The next day I got a form saying I now owed $0. They were very nice to talk to, resolved to issue quickly and I didn't feel they were trying to extract every available dollar.
(started: Feb 2002 --> Completed: May 2016)