1965 Hummingbird with 2 serial numbers

[Oddity]

My Dad gave me his 1965 Hummingbird for Christmas last year.  His step-father (John Pellish) and he custom ordered it from a music shop  in Norfolk, VA in ~1964.  My Dad has been the only owner until now. The custom order details were:  Left-handed; no pickguard etching; wider nut and string spacing.

Here is the interesting bit:  when the instrument arrived all was well except they didn’t make it left-handed per the custom order.  So, he sent it back.  It was returned some time later properly left-handed.

He didn’t notice at the time when it was returned, but upon thoroughly inspecting it after he gave it to me I discovered the interior neck block and the headstock serial #s are off by 2 digits from each other.  #400073 on the neck block and the label, #400075 on the headstock.

Is this something known to have happened or simply a circumstance perhaps related to sending it back to be corrected for handedness when it was new?

Here are a few pics:

https://daleb.smugmug.com/Hummingbird

Cheers

[JO'C]

Are you sure about the year? Serial# suggests 1966. Also 1966 is the year that Gibson switched to the 1 9/16" narrower nut, so if your Dad wanted the wider 1 11/16" nut in 1966 he would have had to order it special. A 1965 would already have the wider nut unless he wanted it even wider, which I'm not sure if Gibson would even do back then. They certainly wouldn't nowadays. A  measurement of the nut width could clear that up. The different serial#'s are likely an employee error. I don't know enough about the differences between right and left handed guitars to know if the neck/fretboard profile  would be the same for both. I'm right handed so I never put much thought into lefty guitars and if they are any different other than being upside down. Maybe they put the wrong neck on the body originally and switched to the correct one when it was returned. 

I'm guessing that you are right handed too based on the strings being installed upside down. Good luck in your quest for answers,

JO'C

[Oddity]

Yes, could have been a ‘65 order and ‘66 construction date.  It was indeed a special order (per my Dad) specifically for the left-handedness, no etching, and wider nut.  (I measured to be sure it is 1 11/16”.)

I did swap the strings around just to play it for a bit, but it’s not being left like that.  (My left-handed son will end up with it.)

Employee error is definitely another possibility for the 2 serial #s.

Looking inside it appears they applied the 2  braces below the bridge pad angled the opposite way as a right handed guitar, and the bridge route is obviously angled opposite for intonation.  Other than that I can’t see anything particularly different.  
 

Thanks!