That's a definite Mdina shape, but perhaps later '80s.
I think Mtarfa and Phoenician used slightly different shapes, and their splodges
tend to have "fuzzier" edges, although that's no rule of thumb.
I would not have thought either Mtarfa or Phoenician - but I've been surprised in the past, I'm sure it will happen again.

Mdina is not always marked.
Especially the very early and most desirable stuff. ('68-'71, the Michael Harris period)
It was a small outfit, it was "all hands on deck", they had trouble keeping the shelves of the shop stacked, so as soon as something was finished, it was straight into the shop with it, to keep things going.
It only got marked once they got hold of equipment to make marks and only then, if somebody spare had the time available to do it.
When labels appeared, they could be used instead of a mark.