Just a thought, Curly... Perhaps we should look at this from the other side. How many No4 trials rifles with the A serials are out there and not ZF marked? If there was such an order, surely they would not have been sold out of service without their final sentence applied?
One with the opposed arrows mark and not ZF'd would prove that.

Bindi, just for $hits and giggles, I'll bring it to Lithgowicon if you're coming.