A revised and updated version of
Abraham Kuyper: An Annotated Bibliography 1857-2010 by Tjitze Kuipers (2011)

You can buy a printed edition of this book on the site of the publisher.

1929

[Letter.]
In: Vijftig jaren Christelijk Sociaal Werk. 1879–1929. Gedenkschrift ter gelegenheid van het gouden jubileum der Afdeling Groningen van het Nederlandsch Werkliedenverbond Patrimonium (vaderlijk erfdeel).
Groningen, Jan Haan 1929, p. 79.

A note from 1906 declining an invitation to speak at a public meeting of the Groningen section of Patrimonium. “From across the entire country,” Kuyper wrote, “I receive day in and out invitations to come and speak. I would do nothing more gladly than fulfill them. But if I accept the one, then I cannot, without being unfair, turn down the other. To my regret, I must therefore disappoint you.” These lines were probably written on a postcard. Kuyper handled a good deal of his correspondence with postcards.