The piercing here is fascinating as the piece weights far too much to be worn as a comfortable ornamental piece of jewelry (almost 2.5 pounds!). I wonder if it was intended for a dedication, say being nailed to the wall of a sanctuary or something similar.
a specimen in trade but not in Haeberlin
These two little videos show how closely both the obverse and reverse of the Rome specimen and the BM specimen match. I’ve never seen two aes grave this close. Traditional wisdom is that molds were not re used, but perhaps this is evidence otherwise? Or could one or both be an imitation?!
The Gnecchi Specimen (another photo of the same) however does not seem to fit:
There is one more specimen in trade but it is SO stylistically different from the BM/Roma one’s I don’t know what to think. The reverse bears passing resemblance to the Gnecchi reverse.
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Other amusements
Aestimata poena ab antiquis ab aere dicta est, qui eam aestimaverunt aere, ovem decussis, bovem centussis, hoc est decem vel centum assibus.
Festus (epitome Pauli), sv. aestimata
Penalties in ancient times are said to be measured in bronze; they valued these in bronze, a sheep a decussis, a cow centussis, that is 10 or 100 asses.
a rough translation of my own
Liv Mariah Yarrow 
A thought: If the mold was made by pressing a previously cast coin into the clay or sand medium then finding two specimens that look similar would still be quite rare but not inconceivable. (In that case, the differences would be in the edges and how well the molten metal filled the mold/casting bubbles, voids, etc.)
Yes, Stamp technology is alive and well in other media at Rome in this period. I rather wonder why we don’t see MORE evidence of it. It would have been a far easier means of creating the molds.