Historical clue formulations

• Accompaniers of cover letters: Abbr. — 2012-08-04
• Letter attachments: Abbr. — 2009-03-30
• Abbr. at the bottom of a business letter — 2007-06-17
• Ltr. extras — 2005-05-20
• Letter attachments: Abbr. — 2004-06-27
• Env. contents — 2001-02-10