$ cat /cf/original.bsdlabel
# /dev/da0:
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
 a: 20144  16  4.2BSD  0  0
 b: 15424   *  4.2BSD  0  0
 c: 35584   0  unused  0  0


$ cat /tmp/new.bsdlabel
# /dev/da0:
8 partitions:
#       size         offset      fstype   [fsize bsize bps/cpg]
 a: 20144  16          4.2BSD    0     0
 b: 15424   *          4.2BSD    0     0
 c:     *             0          unused    0     0
 d:     *             131072  4.2BSD    0     0

$ /sbin/bsdlabel -n -R da0 /tmp/new.bsdlabel
bsdlabel: Offset 131072 for partition d doesn't match expected value 35584
partition d: partition extends past end of unit