Derivation
variable: dpt3date (table[s]: all_vaccination_records [derived table])
variable: birth_date (table[s]: all_vaccination_records [derived table])
gen `vacc'Bprob=0
replace `vacc'Bprob=1 if (`vacc'date<birth_date & `vacc'date~=. & birth_date~=.) | (`vacc'date==. & `vacc'yn==1)