I didn't realize this, but Google Sheets (and I'm guessing Google Docs) as well seems have a limit on the number of named versions you can save?
The bigger issue is that I'm not able to find any published documentation about this limit. I did a search for the exact error message as well as other keywords (related to "named version" and limits) and there doesn't appear to be any documentation that points to this limit.
Below is a screenshot of the error I got today when I tried to save a new named version to my Google Sheets.