Main summary sheet formula
Libreoffice
=IF(VLOOKUP($A3,INDIRECT(B$1&".A1:F42"),5,0)="","YTC",VLOOKUP($A3,INDIRECT(B$1&".A1:F42"),5,0))
Excel 365
=IF(VLOOKUP($A3,INDIRECT("'"&B$1&"'!"&"A7:F42"),5,0)="","YTC",VLOOKUP($A3,INDIRECT("'"&B$1&"'!"&"A7:F42"),5,0))