Remember that the census we use today was not the one on which the census taker took his "original" enumeration.
The census copy that was microfilmed, and eventually digitized, was the "clean" copy that was written by the census taker after he finished taking the census. He used his field notes to make the good copy that we use today.
Any chance there was something in his field notes he couldn't read? And what was the chance that he went down and asked for clarification on an age or place of birth?