That's just Tesla being Tesla, but there is absolutely a way for them to refund your sales tax. They just write you a check for it. It's not your problem how the accounting works internally. They did it for me no problem. But I had also made it 100% clear to them that I'd take the case to the WA arbitration path no problem, and the law was clear here what they owed me.
Here's the thing- Tesla hates being forced down the lemon law path as the car itself ends up with a branded title. So almost everyone ends up with a "buyback" - and during this, that's just a private negotiation between you and Tesla. Which is fine. But you have to know that you have the full lemon law at your back, and if you're not happy with Tesla's offer you don't have to take it. I personally wasn't willing to just let $12K+ in tax and registration slide (don't forget that $1K+ registration in Seattle), but we all have our own logic and reasons during a buyback process. And not every buyback is for a clear lemon law issue.
Every situation is different, but I just sent them a letter requesting a buyback or replacement with my repair records, waited 40 days, sent the letter to the AG and Tesla, had a few phone calls with Tesla, and then dropped it off at one of their locations. Probably less than 4 hours total work. The letter to the AG following the WA Lemon Law process is really the key and lets them know you are serious and know your rights. It's a uniquely pro-consumer process in WA.