If you find a new job and you’re eligible under group insurance, the insurance company can’t deny a claim under pre-existing conditions. This was true before the ACA. What the ACA changed was that insurance companies couldn’t exclude treatment based on preexisting conditions if you go on the open market.
Pre-ACA group plans could deny preexisting conditions for a time period equal to the time that you were uninsured.
When I switched job I would get a letter from previous insurance company stating the dates that I was insured. Once I actually had to provide that to the new company.
