In 2 recent articles I have illustrated why the scope attribute is not needed on data tables with one row or column of th elements, or data tables with 1 row and column of th elements (first row and first column).

2 cheers for HTML tables:
Tables and Beers https://t.co/i026Ov46RR
Tables, Tequila and Beerhttps://t.co/ul98vztjVs #accessibility— Steve Faulkner (@stevefaulkner) January 5, 2019
But what about a data table with an offset column of th elements? Surely scope is needed to differentiate between row headers and column headers in this case?
Table with an offset column of header cells with scope=col on col headers and scope=row on row headers

From looking at the accessibility tree exposed in the browser:
Firefox
A partial view of the accessibility tree for a table, with scope attributes, with offset column of row headers shows that both column headers and row headers are exposed correctly.

A partial view of the accessibility tree for a table, without scope attributes, with offset column of row headers shows that both column headers and row headers are exposed correctly. The same information is exposed as the example table with the scope attributes.

Chrome
A partial view of the accessibility tree (in Chrome) for a table, with scope attributes, with offset column of row headers shows that both column headers and row headers are exposed correctly.

A partial view of the accessibility tree (in Chrome) for a table, without scope attributes, with offset column of row headers shows that both column headers and row headers are exposed correctly. The same information is exposed as the example table with the scope attributes.

Edge
A partial view of the accessibility tree for a table (in edge), with scope attributes, with offset column of row headers shows that both column headers and row headers are exposed correctly.

A partial view of the accessibility tree (in Edge) for a table, without scope attributes, with offset column of row headers shows that both column headers and row headers are exposed correctly. The same information is exposed as the example table with the scope attributes.

Safari (on Mac)
The Mac accessibility tree is different in that it does not expose th elements directly with a role of columnheader or rowheader, instead it defines an array of column and row header items that are associated with a given cell. But as with the windows based browsers, the row and column headers are correctly identified with or without the scope attribute being used.

Conclusion
From testing a range of ‘simple’ data tables with modern browsers, a case where the scope attribute is actually needed on all th elements to disambiguate row and column header has not been found. Have you found one?