Linking Entire Sheet to another Worksheet

I can get behind this analogy, and I see the logic. While I get that excel may need the triangulation like you mentioned, what I don't understand is again, why did it work for me once but not twice to only reference the workbook/worksheet without any columns or rows.

In my original question I said that I only referenced the TW Cash Forecast Mar 26 21 Workbook with the USD Sheet using the following formula in the A1 cell of the tab I want the information to appear on, and it worked.
='TW Cash forecast Mar 26''21.xlsx'!USD

But then when I then tried the below similar formula referencing a different workbook and worksheet I get the #NAME? error.
Here's the link formula to a different workbook and worksheet that is not working:
='CF US 21.xlsx'!CashFlowForecast

So I was able to get one formula to work without the specific cell address but not the other. I don't understand why excel would allow one, but not the other. And like I said, I tried both with both workbooks open and closed to no success.

If I had failed on getting either to work I would assume that I excel required a specific cell address for external referencing to work. But since one of two works, and continues to work regardless of me erasing and rewriting the formula or opening and closing the workbook, I am led to believe that excel allows this type of external referencing, I just have something else wrong.