Extraordinary claims require extraordinary evidence.
We get people with new accounts coming in claiming things like this regularly, and they will always try to argue people into believing them. Because they are attached to the idea that something really was as big as they perceived it. And, they are "defending" the person who they clearly were intimate with. Which is an understandable motivation.
The issue, is that when we are enamored with something, that we are very attracted to, our minds can exaggerate. If a woman (or man) finds a guy very attractive, and he has a big dick, certainly far bigger than average, then it is very natural to perceive it as even bigger than it was.
Also, how something is measure matters—a lot. This contest requires a very specific way of measuring. That is, Non-bone-pressed + Flat ruler + While standing + With the erection perpendicular to the body.
Measure something differently and it is possible to get a wildly different measurement. If a guy has a penis that is even near 9 inches, and he is bone pressed with a soft tape, with a semi-erection, and that tape is measuring along the curve of the semi, and rounded over the glans, to the meatus, then it is possible to pick up to 3 additional inches. But, if that dick is measured with a flat ruler, perpendicular to the body, and not bone pressed, it would be under 9.
That may be the real issue in the "he was 10,11,12 inches trust me bro, I measured" stories. It could come down to personal perception and measuring with a totally different setup like soft tape, bone pressing, and over a curve.