To my knowledge this shape of chalice (with the bell shaped bowl) was only produced during the Harris period.
I am completely in the dark as to whether or not Boffo might have made any between '71 and '77, but most chalices found with dates on are from the mid-later '70s ('74-'79) and are the smaller shape with the straight sided, flared bowl, rather than this bell-shaped bowl.
I do have an unknopped bell-shaped chalice made by Boffo - in Earthtones, but I do not know if he made it at Mdina or at MDG.