Projects with mixed numbered/named references have missing sections

I am retrofitting an old KSS styleguide with the new 'named' indices.

Old numbered indices:
- `Styleguide 1360`
- `Styleguide 1360.1`

New named indices:
- `Styleguide buttons`
- `Styleguide buttons.icon`

The majority of indices in this project are number-based.

When I add a new index which is name-based, this does not appear in the generated navigation bar.

If I navigate directly to the generated styleguide page for `buttons.icon` the name-based index does appear in the navigation.

Reproduce the generated styleguide with both numbered indices such as `1360.1` and named indices such as `buttons.icon`, then compare the navigation bar with the directly generated `buttons.icon` page. Done means named sections appear in the generated navigation alongside numbered sections; no files or tests are identified in the issue.

Written by the indexing model from the issue text.