"edwardsbenj@gmail.com"
This is a known limitation. You can't refer to items in splices that haven't already been mentioned in the source. I don't know why it isn't (prominently) documented, it's definitely part of the folklore.
I'm sure this limitation is documented, I was just oblivious to its implications---naively, the fact that my data declaration wasn't being created by the splice would have seemed to exclude it from consideration. However, your explanation helped me think through the implications, at which point it makes perfect sense---it's not that the declaration is created by the splice, but that it is used in the splice, and must thus be amenable to being fully traversed at the point of the splice, else the splice can't complete its job and compilation can't continue. Thanks again, Mike.