Typically you will only need to complete one background check per organization that you are working with for any given period of time, but all background checks have expiration dates. Some background checks are good for one year and others have a two year lifespan. Additionally, upon expiration of a background check, you will be prompted to complete a new one.
In the rare occasion that you work with two organizations that both use the PH Protect Platform, you will be asked to complete a background check for each one because each organization uses a different background check with different search components and varying expiration dates.