creating a CTE to filter previous CTE populaiton down. How to find new diagnosis of certain ICD 10 code?

The first CTE grabs all patients with the diagnosis codes for substance abuse, the second CTE should filter down to only NEW paitents. Meaning of the people in the first CTE, which of thses people have noy been diagnosised with the 2 codes before. The 3rd CTE grabs all information about the person, locations, date, and age. **In need of figuring out the logic for the 2nd CTE: from diag ... only people who havent been diagnosed before (ie. new/inital diagnosis)**

with diag as (
select distinct d.person_id
, d.encntr_id
, d.diagnosis_id
, d.nomenclature_id
, d.diag_dt_tm
, d.diag_prsnl_name
, d.diagnosis_display
, cv.display as Source_Vocabulary 
, nm.source_identifier as ICD_10_Code
, nm.source_string as ICD_10_Diagnosis
, nm.concept_cki 
from wny_prod.diagnosis d 
inner join (select * from nomenclature
        where source_vocabulary_cd in (151782752, 151782747) --ICD 10 CM and PCS
        and (source_identifier ilike 'F10.10' or source_identifier ilike 'F19.10')) nm on d.nomenclature_id = nm.nomenclature_id
left join code_value cv on nm.source_vocabulary_cd = cv.code_value 
)

diag_final as (
select * 
from diag
--?
)

select distinct ea.FIN
, dem.patient_name
, dem.dob
, age_in_years(e.beg_effective_dt_tm::date, dem.dob) as Age_at_Encounter
, amb.location_name
, e.beg_effective_dt_tm
, diag.Source_Vocabulary 
, diag.ICD_10_Code
, diag.ICD_10_Diagnosis
from (select * from encounter where year(beg_effective_dt_tm) = 2022) e 
left join (select distinct encntr_id, alias as FIN from encntr_alias where encntr_alias_type_cd = 844) ea on e.encntr_id = ea.encntr_id
inner join diag on e.encntr_id = diag.encntr_id
inner join (select distinct * from DEMOGRAPHICS where mrn_rownum = 1 and phone_rownum = 1 and address_rownum = 1) dem on e.person_id = dem.person_id
inner join locations_amb amb on amb.loc_facility_cd = e.loc_facility_cd
where age_in_years(e.beg_effective_dt_tm::date, dem.dob) > 13