How much effort must the Govt make to obtain past performance information?

When conducting a past performance evaluation, how much effort must the Government make to obtain past performance information?

For example, does it need to follow up if a reference provided by an offeror did not submit a past performance questionnaire? Is the Government required to interview or obtain info from the current COR about the incumbent? Is the Government required to consider CPARS data?

Has GAO established a standard for the minimum effort required by the Government to obtain past performance information? I imagine there are cases where an unsuccessful offeror argued the Government should have found/considered negative past performance regarding a successful offeror.