[SQL] SQL Query works for current month but messes up for prior months

I am having trouble with the following query. It is pulling in the correct amounts for July but is off around 2mm in the prior months and has more occurrences than acutal in prior months vs what I am expecting. I am trying to locate the source of the issue.This query is pulling an account and the GL items and amounts that hit over the past 6 months.

Select
gad.ledger_name,
gad.company_code ,
gad.location_code ,
gad.cost_center ,
gad.account_number ,
gad.account_name,
gad.product_code,
gad.channel_code ,
gad.journal_name ,
gad.line_description,
gad.gl_posted_date,
gad.currency,
gad.je_source ,
gad.je_category ,
gad.effective_date ,
gad.created_by,
gad.invoice_num ,
gad.invoice_id ,
gad.invoice_date ,
gad.vendor_name ,
gad.vendor_number ,
gad.invoice_image ,
gad.po_number ,
gad.po_requestor ,
gad.period_name,
gad.amount,
gad.project_code,
rsea.region,
rsea.sub_region
from wbr_global.gl_ap_details gad
left join wbr_global.raw_station_extended_attribute rsea on gad.location_code = rsea.location_code
where gad.ledger_name = 'Amazon.com, Inc.'
and cost_center in ('1172')
and gad.account_number = '60820'
and to_date(gad.period_name,'MON-YY') > getdate() - 186


Here is the output summary of actuals in the GL vs the query.

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