I might be able to answer a little of that.
Background checks are usually run on people when they apply for jobs. Doing a statewide background check is pretty inexpensive but doing several states or a nationwide can very expensive so some companies depend on their prospective employees to be honest as to where they have lived. (smaller companies may not have the budget to run the nationwide checks on many prospective employees.)
If someone has a criminal record but were applying for a job in Alabama and had previously lived with grandma in Texas or California but had nothing in their name such as an apartment, utilities or other bills, paid cash for everything, their names won’t show up unless a specific criminal check is run. If they don’t know where they lived, there is no way to know where to do the background check. People use aliases all the time so a more in-depth check might show the different names which require those names to be run which = $$$.
I worked for a background investigations company years ago. Some things might have changed since then but I do remember the smaller companies not being able to afford all the ‘bells and whistles’ and just wanted the basic checks to make sure they weren’t hiring a serial killer or bank robber.