Hi @willmoin
I don't know if this will help, but it may be something you can show Tier 1 support.
I tested this here in the states, I'm in Illinois.
I setup three columns, two with US Date format, one with the asterisk date and one with out. Then one column for UK dates. What was strange was when in Excel and I switched to the UK date format, I did not have the option to choose with or with out asterisk. See image one.
Image 2 shows the excel sheet. Image three shows the rendering in Canvas.
This tells me that at least some instances of Canvas has the ability to render dates correctly from Excel files based on their cell formatting settings. It suggests, that there may be some difference in the version of Excel for US v UK.
Image 1: no option to choose a date format with asterisk.

Image 2: excel data

Image 3: rendering of excel file in Canvas

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