It appears that there the document version history is limited to 5.
How can I increase this?
Admin / Config / System Settings / Editing / Maximum number of versions
The 'Unlimited versions' option was already selected.
The issue I am having is that when I go to Admin > File Management > right click on document and select 'Version History' I only get 5 items:
The version of CMS is 7.0.586.24.
I found the solution:
Modify the maxVersions field. "0" is unlimited.
This takes effect immediately but only affects new versions e.g. if you reduce maxVersions from "10" to "5" you will still see up to 10 versions until a new version is created and then you will only see 5 versions.
Missing versions do not come back.