Generic material &2 does not have all variants of generic material &1

What causes this issue?

Generic material &V2& does not have all variants used by the dependent
prepacks of generic material &V1&, therefore you cannot copy the
dependent prepacks from generic material &V1& to generic material &V2&.

System Response

The prepack materials are not copied.

How to fix this error?

First add the missing variants to generic material &V2&, then copy the
prepack materials.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.