Buyer network opt outs
Some buyers do not appear in the Query Tool report because they have chosen to not reveal their bid data to publishers.
This can occur for a variety of reasons, though it is most often due to specific contractual agreements that buyer networks have with their customers that prevent them from sharing data with a third-party.
Buyers can choose to not reveal their bid data at any time. However, once a buyer has opted out of disclosing their bid data, this information is excluded for all publishers they transact on.