Just echoing Sinnertwin a bit... a Guinness Record is like AFA grading - they are companies that verify something as official (to their standards). They don't go out finding things to officially verify, people have to bring things to them... and it is not their job to see if others out there have more. If someone does have more, how else can they prove it if they don't apply to have it officially verified by a recognised company like Guinness.
The issue is if a person with a Guinness Record arrogantly (or ignorantly) believes that there aren't any others that are bigger or better.