Luxembourg 1914 - Block Of 4 With Sheet Margin Bearing "Cc" Perfin / Control Punch

Hi everyone,

I recently acquired a block of 4 of the 1914 Luxembourg definitive issue (Grand Duchess Marie-Adélaïde) with a very wide sheet margin.

On the selvage/margin, there is a clear "CC" perfin (perf pattern). I understand that companies used perfins on the stamps themselves to prevent theft, but since this one is strictly on the sheet margin, I suspect it is an official postal control device or examiner's mark (perhaps related to the Haarlem printers or a "Chancellerie" control).

Does anyone have more specific information about this "CC" margin punch for this particular Luxembourg issue? Is it a well-documented control device in the European Perfins catalogs?

Thank you in advance for your help and insights!