GM did sell over the counter 37A replacements that were not stamped. I have one such case in blank form and they are the ideal ones for the re-stampers to find as they don't have to mill the case to remove the old original stamps. Looking at many of the restamps, you can see a ledge behind the mounting boss after they have milled the front case. There's a guy in Indiana who has been stamping them on an original rolling stamp he's acquired from the old AC Delco plant who been turning out some cases that are very close to looking original and it's getting hard to tell some apart.
This is my original AC Delco unstamped case. Ken Bruno told me these old cases have Julian dates on the inside but I haven't taken this one apart yet to see what the date is. I bought this one off eBay to keep it out of the hands of the restampers. That and I wanted the date coded diodes out of it.
