The INDIRECT function indirectly references the sheet names found in Row1 and looks at column F in that sheet, where the COUNTIF takes over and counts matches to the value in A2. The IFERROR returns a blank if any errors occur. IF you do get blanks though, it is not because of mismatches (countif would return a 0 result), it would be likely because sheetnames are not exactly matched... so take a look at that.