Understanding Society User Support

We have some questions about the variable, birth date in the ukhls dataset since WAVE 1
For example, for the Year of birth, all these variables are included in the dataset, but the value are inconsistent, such as
birthy: year of birth;
doby_dv: DOB: Year, derived
dcdoby: correct dob year

Corresponding to the birth date difference, there are different age for the same individual.
May I know which variable I should use to interpret the real date of birth for individuals?