I think it was around the time Vicente Boffo left that polished round pontil marks stopped being used. This is a very nice early bit, beautiful colours. The writing of the word Mdina was done by Marie, Boffo's niece who worked in the factory offices.
With the ink pots, you can tell early from late more by the shape. Early ones have nicely curved sides, like cuddly little slightly squished doughnuts that fit perfectly and satisfyingly into the palms of your hands.
The later ones are less colourful, often a bit taller and have straight up and down sides.