The name of the download, which becomes the name of the .zip file was correct, but the name of the actual .img file inside the .zip was incorrect - it was ignoring the version env var (for the overall image version) and instead using the version of the sdcard repo.
The name of the download, which becomes the name of the .zip file was correct, but the name of the actual .img file inside the .zip was incorrect - it was ignoring the version env var (for the overall image version) and instead using the version of the sdcard repo.