Historical clue formulations

• Trigger, e.g. — 2007-01-20
• Trigger, e.g. — 2002-08-04
• Trigger, e.g. — 2002-04-16
• Roy Rogers's Trigger, e.g. — 2001-10-20
• Trigger, e.g. — 2000-04-29
• Trigger, for one — 1998-10-10
• Popular parade horse — 1998-02-11
• Trigger, for example — 1994-08-06