Historical clue formulations

• 1/20 of a ton: Abbr. — 2017-12-31
• 100 pounds: Abbr. — 2017-10-28
• 100 lbs. — 2015-02-11
• 100 lbs. — 2013-05-09
• 100 pounds: Abbr. — 2012-12-11
• 43.359 kg. — 2009-09-11
• 100 lbs. — 2009-07-30
• 100 lbs. — 2005-08-21
• Portion of a ton: Abbr. — 2004-11-14
• 1/20 ton: Abbr. — 2000-10-22
• 100 lbs. — 1998-01-09