You need to dig a bit deeper and determine the standing as to the collection authority of each debt collector.
A debt collector can purchase a debt, and then assign authority to another debt collector to conduct collection activities on their part.
That is frequently done when a debt collector acquires a portfolio of debt, where one or more accounts are found to involve consumers who reside in states where the purchasing debt collector is not licensed or bonded to collect on their own.
Only one debt collector is permitted to report collection at the same time on an unpaid debt.
That is based on CRA reporting policy, and not any limitations of the FCRA of FDCPA.