They should be in the system. Even released inmates are in the BOP Locator. The only time they are not in there is if they go into protective custody or WITSEC. If that is the case, you will not be able to find them.
https://www.inmateaid.com/ask-the-inmate/for-what-reason-would-an-inmate-who-was-convicted-in-november-2014-still-not-show-up-in-the-federal-inmate-locator#answer
Accepted Answer Date Created: January 03,2015