'in C2
=SUMPRODUCT(--(LEFT([workbook.xlsx]Sheet!$A1:INDEX([workbook.xlsx]Sheet!$A:$A, MATCH("zzz", [workbook.xlsx]Sheet!$A:$A)), LEN(C1))=C1),
            --(LEFT([workbook.xlsx]Sheet!$A1:INDEX([workbook.xlsx]Sheet!$A:$A, MATCH("zzz", [workbook.xlsx]Sheet!$A:$A)), LEN(D1))<>D1))
'in D2
=SUMPRODUCT(--(LEFT([workbook.xlsx]Sheet!$A1:INDEX([workbook.xlsx]Sheet!$A:$A, MATCH("zzz", [workbook.xlsx]Sheet!$A:$A)), LEN(D1))=D1))