Dear respected Mark Rudge,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
As per your description, it seems that the sorts of problems happened when producing Power BI reports from SharePoint card view list.
As you create columns for each quarter and generally, you can use a date column for all items and list, and then group it by quarter in Power BI.
If possible, could you please upload a screenshot for our reference, so we can understand your exact scenario and provide our suggestion in a productive manner, perhaps some related screenshots will be helpful.
Appreciate your patience and understanding and thank you for your time and cooperation.
Sincerely,
Waqas Muhammad