Cyrillic Extended-C is a Unicode block containing Cyrillic characters mostly for facsimile reprinting Old Believer service books. The first 9 characters are (contextual) graphic variants of standard Cyrillic rather than distinct letters.
Andreev, Aleksandr; Shardt, Yuri; Simmons, Nikita (2013-07-20), Proposal to Use Standardized Variation Sequences to Encode Church Slavonic Glyph Variants in Unicode
Andreev, Aleksandr; Shardt, Yuri; Simmons, Nikita (2014-08-06), Proposal to Encode Additional Cyrillic Characters used in Early Church Slavonic Printed Books
Kravetsky, Aleksandr G. (2014-09-27), Letter in support of "Proposal to Encode Additional Cyrillic Characters used in Early Church Slavonic Printed Books"
Anderson, Deborah; Whistler, Ken; Pournader, Roozbeh; Constable, Peter (2022-07-20), "1a Khanty Cyrillic Letter", Recommendations to UTC #172 July 2022 on Script Proposals
Constable, Peter (2022-08-01), "Consensus 172-C4", Draft Minutes of UTC Meeting 172, The UTC accepts U+1C89 CYRILLIC CAPITAL LETTER TJE and U+1C8A CYRILLIC SMALL LETTER TJE
Anderson, Deborah; Goregaokar, Manish; Kučera, Jan; Whistler, Ken; Pournader, Roozbeh; Constable, Peter (2024-04-18), "3. Cyrillic", Recommendations to UTC #179 April 2024 on Script Proposals
↑Proposed code points and characters names may differ from final code points and names