I honestly do not find anything strange in the marks shown by Kristian. The corporate stamp (bollo corporativo) struck twice is not unusual at all, and also the year represented by three numbers is normal.
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The date is difficult to read, but in 1723 it is very reasonable, given that Christopher Mellino was consul in 1722, and that, as we read in the same book of Catello, the corporate stamp stamp ( bollo comuntario) was renewed at the beginning of the year, while the period of the consulate, for the delay in the renewal of the appointments, often it took place at the turn of two years.
Also the shape of the crown is in line with that shown for those years in the book of Catello.
Regards
Amena