I've got the odd finely blown bit of early Mdina too, and the short tortoiseshell I showed is the IoWSG one - it's thicker than the Mdina one - but that was perhaps because the same size of gather was gathered, and so the shorter one ended up thicker. Perhaps estimating the size of gather needed was still something that required refinenent?
It being thin, though does support an IoW attribution.
Is there any way we could be completely off track and it is something outlandish like WMF - I've been convinced WMF was Mdina before. It was a piece mhcgolfclub had for id-ing here.
I hope John turns up and says something.