Have you tried using the YouTube Analytics API ?
Not sure what the equivalent call in the Python library will be, but, for example, this URL will receive watched videos:
https://www.googleapis.com/youtube/analytics/v1/reports ?metrics=views &dimensions=video &max-results=10 &sort=-views &start-index=1 &start-date={first date of interest} &enddate={last date of interest} &ids={your channel id}
You should be able to use the same OAuth token that you use for the YouTube v2 data API.
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