Joined Cases C-773/18 to C-775/18: Judgment of the Court (Seventh Chamber) of 27 February 2020 (request for a preliminary ruling from the Verwaltungsgericht Halle — Germany) — TK (C-773/18), UL (C-774/18), VM (C-775/18) v Land Sachsen-Anhalt (Reference for a preliminary ruling — Social policy — Equal treatment in employment and occupation — Directive 2000/78/EC — Articles 2 and 6 — Prohibition of all discrimination on grounds of age — Remuneration of officials — Discriminatory system of remuneration — Back-pay calculated on the basis of an earlier discriminatory grading — New discrimination — Article 9 — Compensation as a result of discriminatory legislation — Limitation period for the bringing of a claim for compensation — Principles of equivalence and of effectiveness)