Well I’m going to assume that you just got confused by the GAO report and are not attempting to intentionally twist the facts of the report.
In the 72 attempts that law enforcement failed to make a single purchase, they were attempting to purchase under the guise that they were prohibited from owning firearms.
But in the two instances you are referring to (where they were able to purchase an Uzi and an AR-15), they didn’t disclose any information about their legal status either way.
In other words - two completely different approaches. When they admitted to the sellers that they were prohibited from owning firearms, they were 0-72. When they didn’t indicate either way, they were 2-7.
https://www.gao.gov/assets/690/688535.pdf