They don't track by serial number, they track by date completed & customer name. Larry explained this to me several years ago. Gets confusing if a customer has had multiple guns pass though there.
I have a 1915 16ga VH that I bought at auction, the shipping box was postmarked June of 1985 from their location. The person it was sent to turned out to be a semi regular customer. FWIW Larry identified the gun as theirs via the case color. I believe they now send them to Turnbull for CC work.
DelGrego's used the cyanide case color process, rather than the original bone charcoal pack process. The difference between the two processes is very easy to spot. For that reason, I always felt it was incorrect to say they did true restorations, rather than simply refinishing. They seemed quite popular among the Parker collectors community, which seemed odd for a group that supposedly values originality.
I've read that Babe, the elder DelGrego, worked for Parker Gun Co. in the 1940's, hence the mystique. Anyone know if that is factual?