Yes, that is what it says, but that rule is applied after the Versions Data
Exists.  So, first the versions is trimmed by the Versions Data Exists, then
expiration looks at any versions that may be over the "Retain Extra
Versions" days.  You must always set the Versions Data Exists high enough to
accommodate the potential of the Retain Extra Versions.

Remember the backup copy of what matches what is on your system does not
count in the Versions Data Exists.  Versions Data Exists applies to inactive
backups.  The most recent backup is the active backup.  So, if you really
want to keep all backups 30 days.  Just set Versions Data Exists to NOLIMIT
and Retain Extra Versions to 30 days.

Now if you want to keep those same versions 30 days if the file gets deleted
you must set the Retain Only Version and Versions Data Deleted appropriately
to accomplish what you want.