He said he experienced mental and physical abuse while in state care "but that didn't occur in that period they're allowing for".
The 20-year-old, who was born in 1997, was removed from his parents' care when he was 2-and-a-half, so only the very start of his time in state care is covered by the inquiry.
Mr Sade-Inia said he knows of other people who had also experienced abuse more recently than 1999.
He said it wasn't clear to him whether the inquiry would be focusing on abuse from carers, or the services such as Child, Youth and Family.
"I would like to see both of them investigated."
He said he felt like a product in the Child, Youth and Family system, "another statistic on a piece of paper, not a human being".
Former Governor-General Sir Anand Satyanand will chair the royal commission.
The "state care" definition covers circumstances where the state directly ran institutions such as child welfare institutions, borstals or psychiatric hospitals, and where the Government contracted services out to other institutions.
Mrs Martin said that the draft terms of reference approved by Cabinet task the Royal Commission with looking into what abuse happened in state care, why it happened and what the impacts were, particularly for Maori. They also ask the commission to identify lessons that can be learned from this abuse today.
The draft terms of reference would be consulted on before evidence is heard.
Mr Sade-Inia said he would definitely put his experiences forward to help.
He said he hoped the inquiry would use what it found to work towards providing a better system and therefore a better future for children in its care.
