Joined Cases C-72/14 and C-197/14: Judgment of the Court (Second Chamber) of 9 September 2015 (requests for a preliminary ruling from the Gerechtshof te ’s-Hertogenbosch and the Hoge Raad der Nederlanden — Netherlands) — X v Inspecteur van Rijksbelastingdienst (C-72/14) and T. A. van Dijk v Staatssecretaris van Financiën (C-197/14) (References for a preliminary ruling — Migrant workers — Social security — Applicable legislation — Rhine boatmen — E 101 certificate — Probative value — Reference to the Court — Obligation to make a reference for a preliminary ruling)