The goal was to migrate the 100GB to the 128GB, hopefully expand it, and format the 100GB for future temporary/experimental use.
I never planned on having both drives actively running at the same time, so I don't think there should have been any UUID issues, nor did I run across any errors suggesting such an issue.
But even without expanding the partition, the dd command should have 1:1 copied the 100GB, with space to spare, and be bootable, right? Or so I thought...
I had no problem dd restoring the original 128GB contents though, so at least I didn't bork everything. Also the 100GB external USB is still fine. 👍
🤷