A while ago, way back when, National Match meant something as accurizing and the competitions in a nationwide match. The origin of the term National Match was used to refer to a pistol that was built by government armorers with the US Army Marksman Unit. They were built by hand and tuned for the Army Shooting Team for use at the matches at Camp Perry. As the popularity of the term grew, Colt started using the term to market pistols for the retail market.
A very close friend of mine who happened to be an armorer for the Army shooting team gave me a quick lesson on the use and term of National Match and what the N and the M stood for. One day when I asked him the difference between a NM frame (from any manufacturer) and a regular frame. He pulled out a set of letter punches and said "Here is the difference, you can make a National Match frame by stamping the N and the M on the side. Other than the stamp, dimension are only different by the governing geometry to a production gun and the tolerances to which they are held. " If a pistol was rebuilt and tuned by the hands of an armorer for a nationwide match, the pistol is termed as a National Match Pistol.
As time grew, the name stuck and has become a blanket term for those looking to use the term as a marketing tool.
In the case of Springfield Armory, just about every frame is forged and manufactured at Imbel. I was told there is another company that makes components for Springfield that is within the US, but that has not been confirmed on my part. What I do know is the frames that are marked US or sport the Geneseo, IL address in the manufacturing part of the stamp came into the country as an 80% frame and the rails are left to be cut in house. This is for better control over cutting the rails over sized to allow hand fitting by the custom shop or a little closer of a cut for the Operators and other pistols they would like to assemble. Mil-specs and the guns marked Imbel, Brazil were manufactured at Imbel, finished, assembled and even shot outside of the country.
The prefix NM does not stand for "new model" because the model is the 1911-A1 and the 2 letters designate the facility to which the frame or serialized part was made in. At Rock River Arms, their first run of pistols came from the machines at Lewis Machine and Tool. Those first guns have the prefix RR and a 4 digit number. When they discontinued LMT as their manufacturer, they moved to Continental Machine and applied for an alternative variance. The frames were produced with the prefix RA and a 4 digit number.
The model is manipulated into different calibers and different profiles like the Mil-Spec and Operators. A manufacturer can establish a second variance to make more serial numbers or designate different lots of guns...like Springfield did with the TGO series. They used the TGO prefix for all their Letham tribute guns. Those pistols, imported from Brazil as 80% frames, were "manufactured" at the Springfield Armory shop when they cut the rails in the frame and added the serial number.
I hope this helped.
Bob