how to rescue this backup data

Hello. We have a website backup that has to be recovered thanks to 
webserver hard disk crash. However the person who burned the backup seems 
to have done it wrong. This is what we investigated what most likely 
have happened:

a. he have a DVD+R that has a session on it.
b. he created a backup iso image by merging that session:
  $ genisoimage -C ... -M /dev/sr0 -o backup.iso website_backup/
c. he burnt the backup to a /different/ DVD+R that also had a session:
  $ wodim dev=/dev/sr1 backup.iso
   (or, might also have been "$ growisofs -M /dev/sr1=backup.iso" )
d. he happily labeled the DVD+R in /dev/sr1 as "website backup". no 
double check. done.


Now, we have the DVD+R that was there in /dve/sr1 when he do step c, 
because it is correctly labeled as website backup. I can dump backup.iso 
by using this:
   $ dd if=/dev/sr1 of=backup.iso bs=2048 count=155440 skip=1256096
   where value of count and skip are found here
 	$ dvd+rw-mediainfo /dev/sr1 | grep -A 4 '.\[#2\]'
 	READ TRACK INFORMATION[#2]:
 	 Track State:           partial/complete
 	 Track Start Address:   1256096*2KB
 	 Free Blocks:           0*2KB
 	 Track Size:            155440*2KB

We do not know which DVD+R was in /dev/sr0 when he do step b. There are 
a few hundreds in stock. We can locate a dozen that might be if really 
have to. The dumped backup.iso has the right size, that makes me believe 
nothing merged from the previous session in step b are important to me. 
In other words, backup.iso should contain all data I need to recover the 
website.

However, reasonable to believe, I could not mount backup.iso:
# mount -o loop backup.iso /mnt/
mount: /dev/loop0: can't read superblock

My question is, is there a way to recover hierarchical file backup from 
backup.iso, except all files and directories that refer to the previous 
session, which we could not easily find and should not need?

Thanks in advance!

Best.


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