Sheet data without column header lost

If I add some data to a sheet, but don't add a column header, this data is not saved.

### Expected Behaviour

I would expect everything that's entered on a sheet to be saved, regardless of where it's entered.

### Actual Behaviour

Only data in a column that has a column header is saved, data in a column without a header is lost.

#### Steps to Reproduce

For example create a sheet with this content:

Then press reload on the browser and see that the data has disappeared:

Reproduce the issue by creating a sheet with data in a column without a header, then reload the browser and compare the result with the original sheet. Trace the save and reload path for sheet data; done means unheaded-column values persist after reload without changing the existing headed-column behavior.

Written by the indexing model from the issue text.