Such carbines generally have less value than if they had all the original parts. 'Parts gun' usually refers to a GI carbine constructed with various GI parts from different time periods other than the carbine's original parts. If it is, I strongly recommend replacing it with a surplus GI slide. Your slide has a slide lock pin for locking the slide back so it's probably not one of the short slides. Second, National Ordnance used a short slide specific to National Ordnance on some of the carbines they assembled 1962 and later. Especially when compared to the cost of an ER visit. Safety inspections are normally fairly inexpensive. Even if it seems to work fine now it's no guarantee as to the next time. It would be a good idea to get it safety inspected by a gunsmith before shooting it. First, your carbine is a commercial about 50 years old. Commercial parts versus GI surplus depended on availability and cost at the time. The mag catch or safety were sometimes GI surplus. The parts National Ordnance used during the time frame yours was assembled were mostly commercially manufactured parts made for National Ordnance and their carbines. 'All original' from when it was manufactured requires a closer examination of all of the parts. My guesstimate on yours is the carbine was assembled in 1969 or by early 1970. Usually the two dates were within a couple months of each other, but not always.

So there is a date of manufacture of the receiver and a later date of manufacture for the carbine. Keep in mind serial numbers are specific to the receiver and not when the carbine was finally assembled. I can only estimate a date of manufacture. Yours is one of a handful I have records on during that s/n range that are absent the So. El Monte, CA to the left side of the receiver at the front. The one exception being, at about s/n 19023 they started adding So. The markings on your carbine are consistent with those used by National Ordnance from s/n 0001 thru at least 32238 (1962 thru abt 1970).

I've had to reconstruct what s/n and markings were used by gathering whatever info I could over time. National Ordnance records of when serial numbers were used and/or what markings were used, if such records existed, were not shared outside the company.

National ordnance inc m1 carbine