Hi Eric,
As you've probably seen yourself if you've went through the source code, only on creation of a Domain Event Entry is the global index added, just not when fetching the data.
Why this decision's been made, is not completely clear to me, I think Rene or Allard might be able to answer that.
However, as I know what project you're on, I think I can suggest an approach which would give you the global index. That would require introducing your own Domain Event Entry and adjusting the Event Storage Engine (like you've already done) so that when it's fetching events that it also fills in the global index.
Otherwise, you're obviously always welcome to put in a issue, feature request or PR on the AxonFramework GitHub of course.
Cheers,
Steven