A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
The easiest way to do it is to use a formula like this in cell A1 of your (not-yet-hidden) sheet:
=FILTER(Sheet1!A:A,Sheet1!A:A<>"")
and then in A1001 (assuming you have fewer than 1000 entries in column A of sheet1)
=FILTER(Sheet2!A:A,Sheet2!A:A<>"")
and then in A2001
=FILTER(Sheet3!A:A,Sheet3!A:A<>"")
and so on,
and then use this to create your final list:
=FILTER(A:A,A:A<>"")
You can also sort and remove duplicates from that list easily.
As an alternative, you could create a power query against each of your column A values, then combine the queries using the Append Queries function. Then anytime you add data to any of the columns, those tables will expand, and refreshing the data will update the table. But that is a lot more work....