Files from Illustrator 9.x lose all layer names when loaded.
Today I was looking through some old files and discovered that things I drew when Illustrator 9 was the new hotness lose their layer names when loaded; everything is just named "<Layer>".
Observed on several versions from CC2018 (22.x, the oldest one on my computer that I can still run - maybe it's time to delete those older versions I still have kicking around) to 2020 (24.2.3).
I've attached a file that displays this behavior. Ignore the request for a linked file that I didn't include, it's just a scan of a rough sketch.