@colleenyoung and @roch and @loribmt and @naturgirl5 and others interested
Follow up, as far as I can tell double insurance coverage will result in zero charges and I should not have worried, and needn't have inquired.
I am grateful for the clinical services, and the care quality confirmed Mayo Clinic provides exceptional care (consistent with my previous impressions observing health care and quality in my career).
(Side note, I did call for a financial estimate for 2 specialist visits, but learned it can take several (5?) business days for an estimate, so I didn't formally request. Apparently the person I spoke to misunderstood, and I did have a message in the portal, after the visits were completed, indicating the cost and zero balance.)
Best wishes