masand, I think anilbh is actually trying to add a line to /etc/dumpdates that represents the dump that was done.
The -u option was simply forgotten, so the /etc/dumpdates file wasn't updated.
anilbh, using a special "ls" command may reveal the ctime of the dump file, as recorded in /etc/dumpdates.
ls -l --time=ctime --time-style='+%s' dump_file
-l displays more info than just the filenames
--time=ctime makes sure that the ctime is shown, not the last modified time
--time-style='+%s' (see also "man date") displays all timestamps (so the ctime) as the number of seconds since epoch (1970-01-01 00:00:00), as requested in /etc/dumpdates.
So, you can always retrieve all the information that needs to go in /etc/dumpdates.
Using -u when dumping just adds another record to /etc/dumpdates. But you can always add additional lines to /etc/dumpdates directly too (you'll probably need root access).
Using the -T option of dump can work too. It's supposed to get a timestamp in the same format as the format of /etc/dumpdates, so you were spot on with that approach.
If you want to use this approach, use the following steps:
-get the ctime of your dump via the "ls" I explained above
-then add (ie in a calculator) 86400 seconds (equivalent of 1 day) to the ctime you got
-then use dump -T calculated_time