The data used by XKEYSCORE is stored on multiple servers, including the NSA's long term storage servers. How could the Danes be certain the NSA wasn't conductin

The data used by XKEYSCORE is stored on multiple servers, including the NSA's long term storage servers. How could the Danes be certain the NSA wasn't conducting searches from some cache they do not have access to? At the end of the day, this will rely on trusting the NSA despite their dubious history.