It’s common to swap in one Mac for another, using a migration tool to transfer its files and effective identity, or to upgrade a drive in your Mac. But because macOS tracks Macs and drives with behind-the-scenes identifiers (not just their display names), Time Machine can get confused, even if you’re offered a prompt asking if you want to inherit an existing backup set for a new Mac or drive.
If macOS gets it wrong, you have to turn to the Terminal command line and type in text commands to get things back on track.
Macworld reader Richard had a mismatch happen to him when he upgraded to a new Mac by using a Time Machine backup for migration. He was prompted to inherit the old machine’s backup—the one he just used, ostensibly—but macOS picked incorrectly, and shifted him to a completely other Mac’s backup instead, one from 2012.