On 
March 19, 2018, we are updating how 
AdNetworkType1 and 
AdNetworkType2 columns report zero impression rows related to video networks.
Currently, if you request 
AdNetworkType1 or 
AdNetworkType2 columns and request 
zero impression rows by setting the 
includeZeroImpressions flag to true, you get back zero impression rows for 
YOUTUBE_SEARCH and 
YOUTUBE_WATCH values only if you target these networks in your Advertiser account. After this change, we will always return zero rows corresponding to these network types irrespective of whether you advertise on these networks. Other network types are not affected by this change.
This change makes the behavior of 
YOUTUBE_SEARCH and 
YOUTUBE_WATCH network types consistent with the behavior of other network types. Once this change goes live, you may start seeing a higher number of zero impression rows than what you see today when requesting 
AdNetworkType1 or 
AdNetworkType2 columns along with zero impression rows.
If you have any questions about these changes, post them in our 
developer forum.
 - Anash P. Oommen, AdWords API Team
 - Anash P. Oommen, AdWords API Team