I've starred at the following gauge stamps and the only thing I can come to terms with is that at some point Collath had enough influence that the proofhouse at Frankfurt am d. Oder stamped his examples with his cartridge designation or at some point the proofhouse at Frankfurt am d. Oder used his designation??? Or was Wilhelm Collath rolling and proofing his own?

1 bore????

4 bore????

I don't think there were a lot of 1 bore & 4 bore shotshells floating around. Also the odd tubeset knitter's stamp is common to TESCO tubesets from the same time period.
Kind Regards,
Raimey
rse