Someone asked a question of the form: "What makes these words special grammatically, and are there any others like them". link
I am near 100% certain that there is no rule, but, sadly, not infallible, so I preceded my answer to that effect with "I believe".
Another poster aggressively castigated me for posting an incorrect 'guess', although he was unable to come up with such a rule, and eventually admitted that the selection was 'just historic'.
In the first place, I dispute that 'guess' is the correct term. If someone asks if there are any humans over 3 metres, and I say I don't think so, that is a guess. If they ask if there are any humans over 5 metres, saying 'I don't think so', is a lot more than a simple guess.
My thinking in posting the possible answer was that since no one can prove a negative (i.e. that there is no rule), the question would remain unanswered and the asker might waste time looking for something he was not going to find. I was also able to give an example of another class of words, many of which followed the same special rule.
So, my question is: If no one has provided an answer (to a question of the 'is there a rule' type), you are well experienced in the field, and have done some additional research, is it wrong (on this site), to inform the OP of your belief, in an answer?