I observed the following while using the DataTable.
I created the table and used the default column names.
Then I found the Power Automate "Create HTML table" connector that takes a JSON array and turns it into an HTML column (very handy). I used that to convert my DataTables to HTML for emal.
The column names were generic so I renamed all the columns in the DataTables in the forms.
When I added a new row to the datatable, the new row had the new column names, the old rows still had the generic "Column1", "Column2", etc names.
Seems like it would be a good idea to overwrite the whole JSON for the datatable upon each save, so that all of the objects in the array have the "new" column names?