When it comes to a monograde or a motorcycle oil being rated only API SG or similar, I not too sure anything can be read into this. I asked a similar question to oil formulator Weasley recently.
SR5: Weasley, you would know, why are some motorcycle oils the older API SG or SJ, even when a full synthetic and a non-ILSAC grade like 10W40 or 20W50. Yet others have a more modern API SL or SN?
Weasley: Quite frankly because until quite recently the newer API categories were simply not needed. Bikes tend to use higher viscosities and older ones have no catalyst. Most bikes use the same oil in the engine, gearbox and clutch so thin oils are not really wanted - plus bikes aren't under the same fuel economy or CO2 emissions regulatory pressures that cars have been, so no imperative to push the boundaries.