I just joined the chatboards and was really appalled by this thread. The way i see it is that a question was asked and the answers provided were either incomplete or even misleading. Obviously, he double checked and found evidence to the contrary. In this case its natural and healthy to argue.
The liberty dollar in the picture, atleast to me, seems slightly off-centre with the rim going all over the coin and none of the details are omitted as a result of the misalignment. Yet it still is graded as an error by NGC.
Having been a collector for more than two decades I can confidently say that a mint error is never a mint error unless it is labeled as an error by a reputable grading company. People do all sort of things to pass their coins as an error. Many experienced dealers paid a premium for errors that end up being faked.
I say there is no harm in submitting a potential mint error for grading. Simply as there is no other way to find out. Best of luck.
Cheers,
Peter