Historical clue formulations

• Second-most common Vietnamese surname — 2020-04-05
• Second most popular Vietnamese surname (after Nguyen) — 2019-12-01
• Second-most common family name in Vietnam, after Nguyen — 2018-06-15
• Second-most common Vietnamese family name, after Nguyen — 2009-09-13
• Air___, discount carrier — 2007-02-03