[Yaffs] when is the safe time to remove shrink hdr?

shrink hdr is used to identify file hole and deleted files.
for the second situation,if a file deleted without using shrink hdr the
file will appear in the next start.(howyaffswork.pdf says "Shrink headers
are also used to indicate that a file has been deleted and that the record
of the file deletion is not lost.")
but what i am puzzling is that when it is safe to remove shrink hdr?
----
Regards,
Ezio.