Blue Amberol cylinder Oddity ?

[recordmaker]

I have handled one of theses and it seem to be derived from the sub-master mould and will be about 1mm bigger in diameter than the production cylinders and will be at about 196 TPI.
Possibly someone can confirm that.
I assume that the wax sub-master would have been engraved with the additional catalogue number and the working mould made from that wax copy.
The sub-master moulds are repackable so may have been retrofitted into steel shells for these tests and then moulds derived from the actual master moulds used for making the production working moulds.

it really looks like an internal test of back catalogue items rather than special production for a customer or customers.