If a 'Group' posts a v2 (error corrections) file, does this mean that the corrections were made to their v1 file or was it done with respect to all other Groups' files?
The version info for a file is always group based.
So a file marked v2 is the second release of that group.
In most cases that means that some errors in a part the group was responsible for, i.e. the subtitles, were fixed.