I think it's unlikely to be a year date - there is a plastic label, and I think
these are later than the '70's, BUT I'M NOT SURE!
The glass is also very clear - higher quality, and according to the Mdina website, they upgraded the raw materials in '92.
To my knowledge, this is a Michael Harris design, the blue stripes with the yellow texture, and is a design that is one of the Mdina stalwarts - made from the beginning, and still made now. Obviosly, shapes are variations. I do think the square shape is unusual, but being later Mdina, I don't know what they were doing!