Interviewer instructions
The exact date of birth (day, month and year) must be entered numerically for this question. The year of birth of all persons in a private household should be compared with one another, bearing in mind their relationships. In particular, parent's age and children's ages should be reasonably consistent with one another.
[p. 35]
If this question has not been answered and you have been unable to obtain the information by questioning the householder, you should enter your own best estimate of the year of birth. The note about entering such amendments in red should be borne in mind.