The FCS has its own versioning system. You can update (edit) facts, without loosing the old version. The individual versions differ by the version number at the end of every infoID (see -> Meaning of the factID). With the help of the infoID you can also directly link to special versions (see -> Creating links reference).
Using the modify permissions you specify who can edit a fact. Permissions are always assigned to groups.
The attached to download facts files are not stand-alone facts (have no own versioning and GOE). Read details under: Concerning Download Versions.
Warning it is possible that several users work in parallel on new versions of the same fact. These will not merge into one version though. As long as a version is not yet published, its modified contents are not visible.