What are the factors that determine if a file/filesystem is "new" vs
"already there - this is just a new backup".

Given the following scenario:

1.  Box "A" has existing backups.
2.  Create a clone of box "A" - call it "B" .  "B" is identical in *EVERY*
way as far as the filesystem/OS is concerned. Only required changes are
the IP address and hostname.  The DSM.SYS is copied from  box "A".
3.  We turn off box "A" backups and now want to backup box "B"

Would the first backup of "B" consider everything "brand new" and
ignore/flush all existing backups or would it not notice anything
different and just think it is a normal, daily backup?

How can we accomplish this without flushing existing backups or doing a
complete "first pass" backup of everything ?

The boxes in question are Solaris and/or Linux.