The phrase "much less documented" is grammatically correct and can be used in written English.
You can use it when you want to compare the level of documentation of two things and emphasize that one has significantly less documentation than the other. Example: "The smaller island in the archipelago is much less documented compared to the larger, more popular ones. It is a hidden gem waiting to be explored."
Slavery in the Muslim world began long before the Atlantic slave trade but has been much less documented.
The transient character of the dispersive mixing process is much less documented.
Although the effects of spatial and temporal parameter transfer on catchment streamflow predictions have been well studied individually, a direct comparison of these approaches is much less documented.
The effect of climate change on snow in the Pyrenees is well understood, but the effect of land cover changes is much less documented.
While the microstructure of a metal is well-known to affect its equilibrium hydrogen uptake and therefore the hydriding thermodynamics, microstructural effects on the hydriding kinetics are much less documented.
Whereas a large number of dedicated techniques have been recently proposed for static graphs, the design of on-line graph clustering methods tailored for evolving networks is a challenging problem, and much less documented in the literature.
Diagnosed with breast cancer the same week Dina was, I found it far too painful and difficult to even acknowledge the process, much less document it - so I let Dina do it for me.
How many teens go to couture shows or fashion parties, much less document them on their joint Twitter feed, in such a hilarious, uncensored way?" The Brants have almost 70,000 Twitter followers, a fraction of whom appear to be their age.
The spread of millet agriculture into this region is much less well documented, but it is likely that this is due in large part to sampling strategies.
Although it is well known that both mining and agriculture disturb groundwater quality, their mutual interactions are much less well documented, though agricultural activities may prevail once mining operations have ended.
Mate preferences are generally difficult to quantify, so their variation is much less well documented than ornament variation [38], [63].
