As advised to ICANN by the Number Resource Organisation in February 2007, the procedure for maintaining legacy class A addresses (i.e. early allocations made directly by IANA to registrants) is as follows:
If ICANN receives a request to update a legacy Class Record, ICANN will direct the requestor to the RIR for the service region that the requestor resides. The RIR will update the WHOIS record in accordance with its data maintenance procedures. If as a result of this activity, there are changes required in the IANA registry, the RIR will so notify ICANN. In the event, the requestor desires to return the entire /8 to the address pool, the RIR will receive the /8 in accordance with its data maintenance procedures and then will return the /8 to ICANN so that it may be returned to the unallocated IPv4 address pool.