and the PROPER way to install it was with the bond ribbon bent back over the sheath and captured by the box connector, not cut off flush with the sheath.. Inspectors were not happy if they found an end without the ribbon bent back before the anti-short was installed. The bare ground wire solved that, even though the bond strip was still there and best practice was still to bend it back under the cable connector. The "bond strip" in parallel with the coiled sheath had the effect of electrically shortening the length of the "ground" conductor and eliminating the "choke" effect of the coiled grounding conductor when ground fault current existed. This made it possible to use the sheath as a ground. Previously it was not used AS a ground, but was required to BE grounded.
Since MC cable does not have a bonding ribbon as part of it's spec, a ground wire is pretty well a requirement for most applications - virtually all MC cable I've seen over the last 20 years or so has had an insulated ground wire, while the vast majority of the AC cable I've run into (installed since the sixties) has had a bare ground.
Possibly becuase I don't get involved with wiring in the USA, and GENERALLY Canada has higher electrical safety requirements (or at least different ) than the USA.
As for the "BX" designation, WAY back in the 1800s Greenfield had their model "B" flexible conduit, and in about 1900 they brought out an experimental "B" model flex, which had the wires already installed. When it hit the market, according to the generally accepted version of the truth, it was referred to as "B Experimental", shortened on the order sheets to "BX". Might be "BS", but that's the generally accepted story.