For regular TPU Army Reserves, NOT in an AGR position; will the information for each soldier be pulled from HRC (SRB/ARB) or AMHRR for OML?

Short Answer: My Board File
Longer Answer: Look at any MILPER message for an upcoming Evaluation Board and in the details it will spell out OML details. For instance, from MILPER 23-206*

5. Board eligibility criteria (for consideration and placement on an OML).

b. All eligible NCOs will have access to the My Board File (MBF) application and will receive a formal auto-generated email informing them MBF is open to them. All 1SG/MSG who believe they are eligible for evaluation by this board based on the eligibility criteria established within this message who cannot or do not have access to MBF, are responsible for contacting..."
----------------------------------------------
* https://www.hrc.army.mil/milper/23-026

SSG (Join to see), MBF will open and then sometime before the board convenes they HRC "dumps" the relevant documents from iPerms.

I believe the MOU for each board indicates the prices and timeline along with a comment somewhere in there that anything missing in your board file requires a letter to the board you upload to MBF (with instructions how to do so) along with your elections of options statement.

I will have to try to dig up the latest MOU to confirm, but that would be the document you reference.