The Box Drawing block spans U+2500–U+257F, 128 codepoints in Plane 0 (Basic Multilingual Plane). Every one of them is assigned in Unicode 16.0.
All of its characters have the script value Common: they are shared across writing systems rather than tied to one.
By general category: 128 other symbols (So).
The first 128 arrived in Unicode 1.1 (1993).