As of Tableau 9.3 this is now possible (and pretty easy!)
So as long as your data reside in a single workbook (on separate sheets), as you have it, you can use the new union feature....here is a great Think Data Thursday presentation on the subject Think Data Thursday: State of the Unions
In the below image I have a spreadsheet, with identical columns (although if you watch the video you can also union if there are differences), over 2 sheets...one for Jan and one for Feb
I bring my first tab (Jan) into the connect to data, and then by dragging Feb just below, I get the 'Drag Table to Union'
Do this and voila
I know have both sheets appended (and even have the table name as a field)
You can then extract this into a TDE
Hope that does the trick, and makes sense.