Charles Ellicott Commentary Exodus 28:10

"six of their names on the one stone, and the names of the six that remain on the other stone, according to their birth." — Exodus 28:10 (ASV)

The other six names of the rest. —Hebrew, the remaining six names. Either Levi was omitted, or Joseph’s name took the place of Ephraim’s and Manasseh’s.

According to their birth —i.e., in the order of their seniority.