Hello Lars-Åke,

Ok, you are right if local uniqueness is required.

But then I would suggest to use
=C2&"-"&SUMPRODUCT((C$2:C2=C2)*(A$2:A2=A2)*(B$2:B2=B2)*( D$2:D2=D2))
or even
=C2&"-"&SUMPRODUCT((C$2:C2=C2)*(A$2:A2=A2)*(B$2:B2=B 2))

Regards,
Bernd