I have in August 2015 adopted the sigla conventions of the NA28 for the correctors of Codex Sinaiticus in Revelation, and updated my apparatus accordingly:
א* 4th century
א¹ 4th – 6th century (only one occurrence- in 21:4
א² 7th century
א²a 7th century
א²b 7th century
אc 12th century
To download my translation of Revelation.