Veracity of a Marine replacement's dog tags?

[Marine0311]

I was hoping someone could weigh in on these dog tags.

Based on the my reading of Elton Mackin's book, the 138th Co was in the 3rd Replacement Bn, this one shows the 2nd.

Mackin's enlistment date came about a week later after this Marine's. So I wonder where the discrepancy is and if the six digit service number checks out.

 

source: https://stewartsmilitaryantiques.com/us-wwi-usmc-identity-tag-j-titus-138th-co-rpl-bn.50099.archive.htm

[Marine0311]

Rear, showing service number.