I am quite new to creating queries in SEDE, but I am pretty sure one cannot distinguish bounties granted by OP from 3rd-party bounties. Am I right?
Could this be changed?
Now that user information is populated for bounty-related votes, you can compare
As an example, here are the last ten bounties on Stack Overflow (from the last time Data Explorer was updated), with an indication of whether or not they were self-offered.