Board Thread:Theories and Speculation/@comment-24815383-20150827211945/@comment-5273810-20150830184514

Not that the Kakashi Anbu arc is canon but Orochimaru would have 100% seen the Sharingan then as Kakashi was using it during their clash.

Probably something like how Might Guy was at the Chunin Exam at age 6 and didn't become a Genin till 7. A.K.A. A continuity error.