Historical clue formulations

• Pretend to be, at a Halloween party, say — 2022-04-05
• Dress like, for a costume party, say — 2021-09-20
• Impersonate on Halloween — 2020-09-05
• Dress like for a Halloween bash — 2019-01-20
• Impersonate, in a way — 2011-03-20
• Pretend to be, as at a Halloween party — 2008-05-19
• ___-you-please (not tied down) — 1999-01-10