Historical clue formulations

• Correo ___ — 2018-08-24
• Correo ___ (Spanish airmail) — 2017-04-12
• Correo ___ (words on foreign correspondence) — 2017-04-09
• Correo ___ (foreign mail stamp) — 2016-11-27
• Word on mail from Spain — 2013-03-24
• Postal stamp on una carta — 2012-06-15
• ___ di linea (flier to Italy) — 2010-02-13
• Correo ___ — 2009-09-25
• Correo ___ (words on an envelope) — 2007-06-19
• Correo ___ (airmail) — 2007-03-11
• Correo ___ (Spanish airmail) — 1999-09-06
• Word on mail from Spain — 1999-01-11
• Correo ___ (airmail) — 1997-12-28
• Stamp on mail from Mexico — 1996-09-02
• Word on mail from Mexico — 1996-06-19