I might suggest you put a cell in your reference file that you can enter the file name or even a part thereof (like the week number, but in text). Then you can use INDIRECT in your external references. For example, with the value (or text) "3" in cell A1 of the reference file, the following would pull in the value from cell G14 in sheet "Data" in file "A & A Tracker Week 3.xlsx". If the file isn't open, you of course have to add the path.
You can get fancy, if you like, by substituting your WEEKNUM formula for the reference to cell A1 in this if you're always going to refer to the current week's workbook. I personally would put the WEEKNUM formula in A1 in the referencing file just in case you want to refer to another file temporarily. That way, you change the reference once rather than in all the formuals referencing the other file.
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