Accessible tables cannot contain empty cells. The PDF reader is not aware of the table structure but reads whatever Word produces. This means, if you are leaving a cell empty, the PDF reader cannot understand that this cells was left out empty. Therefore, it will read the next value for the following header value.
Here is an example:
In such case, PDF reader might read the second row like "Car A240" or "Car Model". Instead, the empty cell must be filled out with "No car type here". This is what the tool for accessibility accommodate.