Since it is no one's problem, have you attempted to debug through the code to see what is happening or why it's returning false positives? You can find a good start by looking in the /CMS/CMSModules/Content/CMSDesk/Validation/Accessibility.aspx.cs
and /CMS/CMSAdminControls/Validation/AccessibilityValidator.ascx.cs
and a few other controls you will find once you start digging.
Have you tried any external service like Screaming Frog to help with these validations?