The PR_DATA_ADMIN table would be part of Rules schema. During Migrating the Rule tables for split-schema upgrade, this table would be also part of Rules Schema. Because during the upgrade process the PRPC engine would be brought up multiple times and hence it requires the data admin table.
Then why in fresh/new 7.X installation, PR_DATA_ADMIN stay in the data schema?
I think during upgrade process PR_DATA_ADMIN shd be migrated to rules schema, but after when the upgrade done, the PR_DATA_ADMIN of the data schema (old 6.x schema) get used, hence no matter if you drop the table from the rules schema.
Yes you are right Shankha. PR_DATA_ADMIN tables is only used for rule upgrade process. After upgrade is completed if you run the cleanup unused tables from optimize schema wizard it will delete the PR_DATA_ADMIN table from Rules Schema. So it is always recommended to run the cleanup process after the upgrade to avoid all these confusion, this will make sure that you have unique tables in both rules and data schema.
When you do rules schema upgrade in split schema mode, data schema will not be available to upgrade process. Thats the reason PRPC copies pr_data_Admin table from data to rules schema only for upgrade process.
pr_data_admin table in data schema gets upgraded seperately when you do standalone data schema upgrade.