Historical clue formulations

• Distinctive mark — 2024-12-27
• COPY, perhaps — 2022-10-15
• OK, in a way — 2022-02-26
• "Forever" purchase — 2022-01-03
• 77-Down is on the most collected one in U.S. history — 2021-09-12
• What takes a licking and keeps on sticking? — 2021-08-27
• Benjamin Franklin is depicted on the first U.S. one (1847) — 2021-03-31
• It may say "Forever" — 2021-02-22
• One might be forever — 2021-01-29
• Really put one's foot down — 2021-01-10
• Part of a philatelist's collection — 2020-12-16
• One stuck in a corner? — 2020-05-30
• Impress — 2020-05-15
• Post office purchase — 2019-05-20
• Philatelist's buy — 2017-01-24
• "PAID," for one — 2016-08-31
• Passport certification — 2016-02-23
• - — 2015-06-21
• "Approved," e.g. — 2015-05-02
• Purchase that's canceled — 2011-12-18
• Forever ___ — 2010-11-20
• Perforation site — 2010-06-24
• Sign of approval — 2008-05-25
• Notary's item — 2008-02-27
• Pouting person's action — 2008-01-27
• Post office purchase — 2007-06-11
• Show impatience, in a way — 2007-03-24
• Snail mail attachment — 2005-09-20
• Envelope sticker — 2004-01-26
• Approval sign — 2004-01-11
• It may make an impression — 2002-06-29
• Passport feature — 2000-10-31
• Express displeasure — 2000-05-06
• Kind of pad — 1999-03-17
• Approval — 1996-07-03
• Characteristic mark — 1996-04-24
• Approve, in a way — 1996-02-09
• It may travel first-class — 1995-10-27
• Item in 5-Across — 1995-10-02
• It goes in a corner — 1995-04-28
• 33-center — 1995-04-16
• Philatelist's item — 1994-09-13
• Notary public's need — 1994-02-16
• Philatelist's item — 1994-02-09