No.

John and Gerry, who are walking along with a clearly visible number written on their foreheads, have to know a certain number range, thus the upper limit and the lower limit of the range of their numbers, and they have to know another aspect, for example: a possible sum, a possible difference, a possible product, a. possible quotient of their two numbers (for instance: Gerry only knows a sum of the two numbers of a certain number range, whereas John only knows a product of the two numbers of the same certain number range). So they know enough, even more than enough (!), in order to solve the riddle.

The primises in the riddle “Perfect Logicians” are enough too. Again:

Perfect Logicians.

Players A and B both have got the number 12 written on her forehead. Everyone sees the number on the front of the other but does not know the own number. The game master tells them that the sum of their numbers is either 24 or 27 and that this numbers are positive integers (thus also no zero).

Then the game master asks repeatedly A and B alternately, if they can determine the number on her forehead.

A and B know enough in order to solve the riddle.

If it is said that two humans see a number, then we can surely assume that this humans are capable of seeing and reading, and of knowing what they see and read. That is common sense.