The Combining Half Marks block spans U+FE20–U+FE2F, 16 codepoints in Plane 0 (Basic Multilingual Plane). Every one of them is assigned in Unicode 16.0.
By script: Inherited (14), Cyrillic (2).
By general category: 16 non-spacing marks (Mn).
The first 4 arrived in Unicode 1.1 (1993); later additions came in 5.1 (3), 7.0 (7), 8.0 (2).
Most characters here are combining marks. See combining diacritical marks.