BDH override pricing source doesn't change prices

[arbitrager44]

I have the code below to pull the historic prices from a set of corporate bonds. If I run the code, the price output is exactly the same despite the overrides. If we look at the prices in BB using a simple HP and changing the source, the prices are indeed different. What am I doing wrong here?

import pandas as pd
import datetime
import pybbg
import numpy as np

con = pybbg.Pybbg()
cusips = ['00774MAC9 Corp', '20848FAA8 Corp', '073685AD1 Corp', 
		'032654AJ4 Corp', '03027XAM2 Corp', '92343VER1 Corp',
		'92343VES9 Corp', '952845AE5 Corp']

end_dt = datetime.date.today()
delta = datetime.timedelta(days = 180)
st_dt = end_dt - delta
st_dt = st_dt.strftime('%Y%m%d')
end_dt = end_dt.strftime('%Y%m%d')

trial_1 = con.bdh(cusips, 'Px_mid', st_dt, end_dt)
trial_1.sort_index(inplace=True)
print(trial_1)


trial_2 = con.bdh(cusips, 'Px_mid', st_dt, end_dt, 
		overrides={'Pricing_source':'BVAL'})
trial_2.sort_index(inplace=True)
print(trial_2)

trial_3 = con.bdh(cusips, 'Px_mid', st_dt, end_dt, 
		overrides={'Pricing_source':'TRAC'})
trial_3.sort_index(inplace=True)
print(trial_3)