I added the following to src/UPDATING

20040109:
        Compatibility for old ffs superblock layouts has been
        added, and the restrictive fsck checks have been reenabled
        when using those layouts.  If you have been using -current
        since 20030402, you may find that fsck again signals fatal
        superblock mismatches.  To work around, you can use
        fsck -b 32 to restore an alternate superblock.

See the following message to tech-kern
 <URL:http://mail-index.netbsd.org/tech-kern/2004/01/05/0011.html>

or pr's port-macppc/23925 and port-macppc/23926 for more details

See pr 23925 or 23926 for more details
 <URL:http://www.netbsd.org/cgi-bin/query-pr-single.pl?number=23925>
 <URL:http://www.netbsd.org/cgi-bin/query-pr-single.pl?number=23926>