You must be referring to the Gemara on 11b which suggests that the killer (not the Go'el ha'Dam) may not leave his Ir Miklat until all three types of Kohanim Gedolim die; the one anointed with oil, the one that was non anointed but simply "chosen" to wear the eight garments of the Kohen Gadol, and the temporary replacement Kohen Gadol. The death of a single one does not suffice; all must die for the killer to leave his Ir Miklat.

The question arises that oil was used to anoint Kohanim Gedolim only before the time of King Yoshiyahu. Afterwards, the Kohanim Gedolim were chosen to wear the eight garments but not anointed with oil, as Rashi explains on the Mishnah. So how can both an anointed Kohen Gadol, and one chosen without anointing, live in the same period?

The RAMBAN (Vayikra 16:32) and RITVA (Makos here) explain that even before Yoshiyahu, a Kohen could be chosen but not anointed. This would happen when the original, anointed, Kohen Gadol was still alive but another had to be appointed temporarily for some reason (i.e. as a Yom Kipur backup just in case the Kohen Gadol became Tamei - Ramban - or because the Kohen Gadol was taken captive but still alive - Ritva).

Best wishes,

Mordecai Kornfeld

Kollel Iyun Hadaf