It's really wierd to me that the serial number falls in the 1957 build time but the vol pot is Dec 1959. I believe those were original pots too.
I wish you'd taken the neck off... just 4 bolts and goes back on easy. The date code on the neck would have given the whole story.
The way to look at the pot codes is that if you believe they're original to the guitar, the guitar (or amp) could not have been made
before the date on the pot.
The guitar most often was assembled weeks to months after the pot date code, rarely years after. But that still happens; when I worked at Gibson, bulk parts like pots, switches (even their pickups) sit in large bins until the folks building wiring harnesses pluck them from the bin for assembly. If you had a pot at the bottom of that bin, and they refill the bin before it is completely empty, then it's possible for there to be a couple pots that don't get used for a year or more after manufacture, even as the bulk of parts spend very little time waiting to go into a guitar.
You shouldn't put too much stock in the serial number either. You might have noticed when you looked up the number on a chart that
there's overlap of serial number ranges among some years. Serial number date charts for vintage guitars were assembled by observation, where dealers/collectors date the instrument from other information (pot codes, neck date, pickups, details of construction, etc) then record the serial number and attempt to correlate the # to a date range.
Reliable serial number to date information probably began when Gibson (and other makers) included the year of manufacture as part of the serial number. I know Gibson was doing a version of this by the 80's, not sure when exactly they began it. Each manufacturer has their own method, and they probably weren't motivated to have a rigid serial number system until they chose to use that number to track quality control and record returns to the factory.