Seems pretty specific to span two centuries of known construction. Why would they be saved and not recycled? Nearly every medieval village had a blacksmith, with larger population centers supporting more, within the whole of medieval Europe thousands of blacksmiths at any one time, so why have only 116 of these turned up when there should be hundreds of thousands of them?
I think it's very interesting their construction appears to cease just in time for Christianity to take over Europe in the late 4th century. Previously, Rome had 12 principal deities.
So, if we're talking about casting, then we have to ask what did they cast in, and what did they use for the molded object? I don't know when sand casting was invented, but I think that's how a lot of modern casting in bronze is done. As for the original piece that was molded, you could do a lost wax type process, and wax was certainly a thing available back then, but would it have been used for this purpose? And how would you do lost wax with sand casting? If it wasn't a lost wax process, then how did you get all those neat little knobs, because otherwise you'd get the equivalent of mold tear outs.
Any sand casted piece would have needed a lot of cleanup to make it look nice, so you'd need to cut, sand, and polish those edges and surfaces.
It would be interesting to have this discussion with someone who is well acquainted with the process of casting bronze, to see what their thoughts are.