i would just copy the first 3 sheets of datas column A data to your combined tab.
Then highlight column A on your COMBINED tab. Go to DATA Ribbon at top of screen. Select REMOVE Duplicates. Then hit ok.
This will get you a unique master list. Then put the following formula in cell A2 and drag down:
Formula:
=IFERROR(SUMIF(Sheet1!$A$2:$A$50,COMBINED!A2,Sheet1!$B$2:$B$50),0)+IFERROR(SUMIF('Sheet1 (2)'!$A$2:$A$50,COMBINED!A2,'Sheet1 (2)'!$B$2:$B$50),0)+IFERROR(SUMIF('Sheet1 (3)'!$A$2:$A$50,COMBINED!A2,'Sheet1 (3)'!$B$2:$B$50),0)
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