THERE IS NO SUCH THING AS AN "NS10"
The confusion commonly encountered when referring to these famous monitors, mostly surrounds the 1978 original (correctly called the NS-10M, not NS10) and one of the 1987 upgraded models (correctly called the NS-10M STUDIO, not NS-10MS, or ns10ms, or NS10s, or anything else).
This confusion stems from a) common miss-use of the name(s), b) tricky grammar, and c) misleading sales descriptions:
a) Common Miss-use of the Name
The correct name of original 1978 Yamaha monitor is NS-10M. Officially, there is no NS10, ns10, ns10m, or pairs of NS10's, NS10MS, ns10's etc.. There was a brown, hi-fi “NS-10” (no "M" at the end) which came out in 1970, but has no relation to the monitors used for studio work.
The correct name is in all capitals (upper case), there is a hyphen after the "S", and there is an “M” at the end. Of course, we all write and/or talk of an “ns10” or a pair of ns10's (etc), but what we are usually really referring to is the original NS-10M.
Furthermore, the later models ALL have NS-10M as the basis of their name (e.g. “NS-10M STUDIO”, “NS-10M PRO”, “NS-10MX” etc.).
b) Tricky Grammar
The plural / apostrophe problem combined with misspelling. This one creeps in on almost every forum thread. People write of their “pair of NS-10M’s” or "a pair of NS10s" or how much "ns10s' suck" (or other miss-spelled variations thereof) and these somehow get mistaken, along the way, as an abbreviation of "NS-10M STUDIO", which is a different monitor altogether. NS-10MS (or ns10's, ns10m's, etc.) does not equal NS-10M STUDIO. Yamaha once named a pdf manual for the NS-10M STUDIO "ns10ms.pdf", but this was simply a file name and not an official abbreviation. The NS-10M STUDIO was never officially abbreviated to NS-10MS (and the NS-10M PRO was never abbreviated to NS-10MP either).
c) Misleading Sales Descriptions
The NS-10M STUDIO model is generally considered more valuable than the older, original NS-10M, as is the NS-10M PRO model. Thus, people selling their original 1978 NS-10M monitors will often include the words “studio” and/or “pro” in the title or description. This helps their item get hits from those more desirable search terms. Also, because of the confusion most people have regarding the naming of the various models, this may (intentionally or not) mislead customers into thinking they’re buying a more valuable NS-10M PRO or STUDIO model, when in fact they are not.
Here are the correct names of the six monitors:
NS-10M PRO (1987)
NS-10M STUDIO (1987)