I thought they had an ASED- an assessment expiration date. 3 years from the time u filed. Within that time if they sent u a letter, then there’s still the expiration. Mine has been held for almost 3 years bc I claimed my kid for the first time and I’m owed a lot of money back. I sent them everything 2x and physically went in 2x. It’s been 1.5 years since I got the letter where they said they made the correction- which was more $. I’ve seen they reviewed it and still no issues.
