Clarification on MJF rule for claim parents as dependent?

Hi all--appreciate any guidance.

I contribute about 70-80% of my parent's financial support, which I am of course happy to be able to do. They draw SS, and have only trivial other income (less than $5200). They file MFJ.

Everything I've read says I cannot claim them as dependent if they MJF, with the caveat that: Your parent, if married, doesn't file a joint return or files a joint return only to claim a refund of income tax withheld or estimated tax paid*.*

Is the exception to the MFJ rule that simple? Basically, with any earned W2 income (where there was withholding), or 1099 income with Estimated payment, they can file MFJ and I can claim them as dependent (presuming they would get a refund from their MFJ filing)?

As a secondary question (assuming the answer to the above is "yes"): their past trivial refunds (in the $100-200 range) have been held back by the IRS for years toward a federal tax debt. Does the fact that a refund they'd be entitled to would be directed toward that outstanding balance change the above assessment?

thanks for any thoughts, and appreciate it