Another recent study of the pirate academic site Sci-Hub, “Sci-Hub and LibGen: what if… why not?”. On a thoroughly randomised sample of articles, found via 55 different commercial databases recommended to students at McGill University, Canada…

the overall retrieval rates for the 2,750 samples, as of July 2017, is pretty good. The full-text retrieval rates for both Sci-Hub and LibGen are respectively 70% and 69% […] At the discipline level, the results are showing the lowest retrieval rates in Sci-Hub for Law (20%), Music (28%) and Business/Management (32%). [while] five databases (9%) are showing a 100% retrieval rate (British Humanities [Humanities Index, nowadays tracking around 400 titles from the UK and Commonwealth], Elsevier ScienceDirect, Sage, Springer and Wiley) coming from the following disciplines – Humanities and Multidisciplinary.

“100% retrieval rate” for the Humanities Index seems odd. Although looking at the titles list of current actively indexed titles, it seems possible for the 318 “Core coverage titles”. Though I’m not sure you’d be picking up many articles at Sci-Hub from newspapers such as the Times Literary Supplement or trade journals such as Town and Country Planning.