I have created rollback segment with following command

CREATE ROLLBACK SEGMENT RB15 TABLESPACE RBSDATAA STORAGE (INITIAL 3M NEXT 3M OPTIMAL 70M MINEXTENTS 20);

when i query dba_rollback_segments

query shows me AS

INITIAL_EXTENT 62914560
NEXT_EXTENT null
MIN_EXTENTS 1
MAX_EXTENTS 32765

Query shows different storage value.

what is the reason?