What's the difference here?
Are stateful IPv6 entries retained in the DHCPv6 server?
Stateful autoconfiguration of IPv6 is the equivalent to the use of DHCP in IPv4. It requires a DHCPv6 service to provide the IPv6 address to the client device and that both client device and server maintain the "state" of that address (i.e. lease time, etc).
Stateless autoconfiguration of IPv6 allows the client device to self configure it's IPv6 addreess and routing based on the router advertisements.
A network can use both stateful and stateless autoconfiguration at the same time, they are not mutually exclusive.
If you are interested, for more detailed information I would highly recommend you read RFC4862.