Metadata corrupted after Sequoia update

Upon updating to Sequoia 5.1.1, the metadata on many files has become "incorrect": many (but not all)

files now have a creation date like "January 24, 1984 at 00:00" or "December 31, 1979 at 23:00"' to give two examples. Some of these files are the latest files I was working on, but others are files I haven't touched in years. At least 563 files have an incorrect creation date.

What can I do?

I have applied "First Aid" on the hard drive using the Disk Utility app.

I notice that after updating to Sequoia 5.1.1. the main volume has been renamed in a way that looks unusual compared to the naming convention of 5.1.0. Here it is for reference.

Does this look normal?