It appears that Spain did not adopt the 1969 CIP standards until at least after 1974

Proof certificate from 1972; still with 900 kg/cm2.
"This shotgun has been proofed with two equal firings through each barrel with a pressure of 900 kg/cm2 at 17mm (about 3/4 inch) from the face of the breech."

[Linked Image from photos.smugmug.com]

1100 kg/cm2 (15,646 psi) proof receives 4 shots through each barrel.

CIP certificates state "Esta escopeta ha side probada con dos disparos iguales por cada canon, desarrollando presion de 960 bar a 25mm. del plano de culata." (1 inch)

1974 date code Sarasqueta with 900 kg

[Linked Image from photos.smugmug.com]

https://sites.google.com/a/damascusknowledge.com/www/home