Historical clue formulations

• Telephone no. add-ons — 2025-06-05
• Tel. number add-ons — 2021-07-22
• Personal organizer nos. — 2019-03-09
• They're added on bus. lines — 2018-03-18
• Tel. no. add-ons — 2017-01-29
• Tel. no. add-ons — 2016-07-26
• Office nos. — 2013-03-24
• Parts of office tel. nos. — 2011-05-02
• Company lines?: Abbr. — 2011-04-23
• Bus. phone components — 2001-03-04
• Office phone nos. — 1997-06-15