Yes we have the same issue. I think the API returns the username for an inactive account in a slightly different form which is what causes the discrepancy.
As a workaround we have added a custom personnelAlias aliasPool value called SAILPOINT_ID to our Cerner accounts.
Then we are using a customization rule to parse that value out of the personnelAlias and populate a custom field I added to the Cerner Schema in Sailpoint. (This allows for easier Correlation)
We haven't been able to get all of our Cerner accounts populated with the new personnelAlias value. but I am populating that value as I touch and provision Accounts. so moving forward we should be able to correlate more and more of the Inactive accounts.