Historical clue formulations

• Tacks on ... or, when parsed as two words, what 17-, 28-, 47- and 63-Across all have? — 2026-04-06
• *Book addenda — 2025-10-16
• Tacks on — 2020-06-28
• Subjoins — 2004-11-13
• Adds on — 2001-09-02
• Attaches — 1996-05-17
• Adds a rider — 1994-12-11
• Attaches — 1993-12-26