Has there ever been a definitive list of Effector serial numbers published? Or is a letter showing shipping to Jovino's the only real way to "prove it"?
The gunsmith at Jovino's that made these Effectors only modified new in box guns, according to what he told me. Which means that if you get a letter for a particular gun and it states the revolver left the factory as a 6inch .44/.45/.41Mag, delivered to Jovino's in NYC, but it's clearly a 2.5inch snubby sitting in your hands now, it's safe to assume the provenance is real that it passed through the Jovino storefront and had been modified there.
While it's conceivable the gunsmith at Jovino's could have customized one-off examples of customer provided guns this would have been exceedingly rare, and only a Jovino invoice receipt could prove provenance in that case. I have two such guns, but the gunsmith was more than a friend of mine, he was a tutor. The whole point of the snubnose customization was so that the Jovino storefront (who also sold nationwide in quantity as a S&W distributor/authorized dealer) could offer up a "Jovino exclusive" that you could only order from them (in addition to having other things in your order, of course). So merely offering the conversion to snubby on a walk-in customer provided gun would defeat the purpose of being exclusive.
Nonetheless, the experience of the Jovino gunsmith himself, having been a bonafide licensed gunsmith in the City of New York for some four decades, I suppose is what makes these interesting and desirable.
He officially retired from the profession this month, September and has moved out of New York City. No more Effectors will ever be made in this town and the City has likely lost the last of it's truly competent Old World gunsmiths.