For centrelink purposes I can't make a claim for FTB until both DH and I have lodged out tax returns. Then when we do that we find out fairly quickly how much FTB we were entitled to from the year before.
There are other reasons for your DH to catch up with his tax. My ex didn't put his in as he knew anything he was owed would come to me in child support arrears. They eventually caught up with him and he was fined.