[kerryusama04]

How does someone being honest by saying "may have" when he's not 100% sure decrease his credibility or gravitas?

Because of the first time the subject was mentioned, it was mentioned definitively.

The crater, buried beneath a half-mile of ice and discovered by some serious airborne and satellite sleuthing, is more than twice as big as the one involved in the demise of the dinosaurs.

[Ichneumon]

[How does someone being honest by saying "may have" when he's not 100% sure decrease his credibility or gravitas?]

Because of the first time the subject was mentioned, it was mentioned definitively.

Again, no, it wasn't.

[Virginia-American]

I could have sworn I already posted this, but I don't see it anywhere

Mentioned definitely as "the one involved in the demise of the dinosaurs." not as "the one that killed the dinosaurs."

That's a big difference.