Bizarre/incorrect results when querying Bing News API?

Question

I'm using the Bing News API to collect counts of news articles over select time periods.

However, I'm getting larger counts when I reduce the time period for some reason - when I tell my code to collect counts for 6 weeks after February, I get a smaller number than when I tell it to collect 3 weeks worth of data. What might be the problem?

import time
from datetime import datetime

api_key = 'MY API KEY'

endpoint = 'https://api.bing.microsoft.com/v7.0/news/search'
headers = {
    'Ocp-Apim-Subscription-Key': api_key,
    'Accept': 'application/json'
}

search_term = 'MY SEARCH TERMS'
count = 100
start_date = datetime(2022, 2, 24)  # Set the start date

total_articles = 0
while start_date < datetime.now():
    end_date = start_date + timedelta(days=42)  # Define a time range 
##Here is the problem: when I select 21, i get a larger number than when I do 21

    payload = {
        'q': search_term,
        'count': count,
        'freshness': 'Day',
        'mkt': 'en-US',
        'from': start_date.strftime('%Y-%m-%dT00:00:00Z'),
        'to': end_date.strftime('%Y-%m-%dT00:00:00Z')
    }

    response = requests.get(endpoint, headers=headers, params=payload)

    if response.status_code == 200:
        news_data = response.json()
        total_articles += news_data['totalEstimatedMatches'] if 'totalEstimatedMatches' in news_data else 0
        print('Processing....')
    elif response.status_code == 429:
        print(f"Rate limit exceeded. Waiting before making the next request...")
        time.sleep(10)  # Wait for 5 seconds before making the next request
        continue  # Retry the same request after the delay
    else:
        print(f"Request failed for date range {start_date} - {end_date} with status code {response.status_code}")

    start_date = end_date

print(f"Number of articles about {search_term}: {total_articles}")