Springfield's Loaded models, could either have the N or NM prefix. Model's with the N prefix are imported almost complete with the exception of the sight and beavertail grip safety cut's. These cuts are done at Springfield's facility in Geneseo, IL. The NM prefix Loaded's (as well as the TRP and Trophy Match) have the magwell and most of the internal cuts done, but no rail cuts. The final CNC machining on NM prefixes is done in Illinois. This information was from this article.
The rest of the 1911 prefixes such as LW, TGO-2, TGO-3 and EMP all come from Springfield's Illinois facility, though I have seen Champion LW's marked "Brazil". The Custom Shop gun prefixes such as CRG, FBI, DEA, and TGO-1, as well as any other Custom Shop marked gun, are also made in Illinois. According to Springfield, the Custom Shop marked guns are built using "National Match" frames.
Springfield uses the prefixes of "N" and "NM" to designate 1911-A1 type pistols, just as we used "AM" as the prefix for the P9 series of pistols. The only pistols which use the national match frames are the complete custom pistols built through our custom shop. These pistols have "Springfield Custom" etched on the slide, and will have the "NM" prefix to the serial number.
Deb, Custom Shop Coordinator
Is there a difference in build quality? In my opinion/experience...yes. In general the NM marked guns have a better frame/slide fit, than the similar model with a N prefix. Other's on the internet tend to look for the NM marked 1911's as well.