In the matrix he can be identified either by his initials KG, or by 4 digits, like e.g. 12C1.
The first 2 digits stand for the week the record was cut (01 to 52)
The C is the first initial of his full christian name;
The 1 means that it is the first cut (2 stands for the second cut respectively).
While the 4 digits can be found on nearly all his cuts between 1972 and 1990, KG was only used for cases where cuts were shipped without engraving the catalog numbers but only marked as A and B on the outside of 14" master lacquer (used between ca. 1980 and 1990).
Kees Grijpink worked since 1996 as an assistant principal and digitization of audio studio at the Meertens Institute in Amsterdam.