As nobody else has replied I will have a go....
I only have the same book as you for reference but, as far as I know the use of the term 'seaweed' is (like many others e.g. 'axe head') an internet term that somehow takes on a life of it's own and then is repeated ad infinitum (there is probably a thesis in this phenomena). I only know this colourway as 'blue green'.
The shape I would agree (again using Mark Hill's book as reference) would be post 1972, more angular and less rounded, as to precisely when I am afraid I am clueless (a familiar state of affairs). I do not know when Mdina stopped making these, if at all.
A lovely vase taking considerable skill to make, I tend to think a few items from Mdina always look good displayed together.
If you get bored of it let me know...... (just joking).
An extra note, an item being unsigned is no indication of date or production period, many items were unsigned for a wide variety of reasons.