My understanding of the signatures is that virtually nothing was signed during Michael Harris' time there (other than the very few pieces he signed with his name) because he didn't allow it and that the pieces with the word 'Mdina' to the bases are post MH. However, I've not yet seen an early or late piece with the unfinished base that yours has - I have a very early piece with the polished pontil (unsigned), I have several early pieces with the ground flat bases (also unsigned) and I have some later pieces with the ground flat base (signed) but not one with the broken off pontil which is why I suggested it might be a second.