perhaps the 6152 is the rarest followed by the 6154 and 2/56.
There are more 3646s or 6152/1s then all of the above combined.
Of the 3646s delivered to the Italians and Germans, many were destroyed, ruined by water or lost at sea. Precise numbers are impossible to determine. Until someone shows delivery notes from Panerai to the Regia Marina or from 1946 to the Marina Militare, we are holding opinions.
Cheers,
Asi