The naming convention for variables is the same as for data files, that is, the same variable across waves has the same root name but a different wave prefix. So, the variables for derived age in Wave 1 is a_age_dv, in Wave 2 is b_age_dv and so on.
If a variable does not change across waves it will not have a wave prefix. One example is the unique individual cross-wave identifier pidp.
