Historical clue formulations

• 2016 subject that dominated U.K. newspapers — 2025-06-10
• Event of 1/31/2020 — 2024-03-02
• Campaign promise of Boris Johnson — 2020-02-04
• Subject of a 2016 U.K. referendum ... or a hint to 16-, 25-, 41- and 55-Across — 2019-09-25
• Portmanteau in 2016 world news — 2017-02-22
• Subject of a notable 2016 referendum — 2017-02-09