Hi Meagan, One anomaly in a hiring practice isn't uncommon. For this situation, the best practice would be to include those applicants that you did review in the pool for analysis along with those from the 3rd party recruiter's data. Those that applied after the position was outsourced can be dispositioned as "not considered" - and they are not applicants if you are using the internet applicant rule. If you have only certain dispositions in your system and "not considered" is not one of those, then it is certainly fine to choose another as long as that disposition is equivalent to "not considered." You could also enter a note or comment to explain that these candidates were not considered.
You can use this OFCCP audit checklist to ensure you're doing what is required to maintain OFCCP's regulations including VEVRAA, Section 503, and EO 11246. Or request a demo to streamline your compliance and recruiting efforts.