It's simple. Selective will rollback only changes in the selected rollback id, but rollback configuration will rollback all changes before this configuration id. In the example below, rollback selective 2 - will not rollback changes in 0 and 1 ids (int ge0/5 shutdown):
vEdge1(config)# rollback selective 2
vEdge1(config)# show configuration
vpn 2
router
ospf
area 0
interface ge0/5
network point-to-point
exit
exit
!
!
no interface loopback2
!
vEdge1(config)# exit
Uncommitted changes found, commit them? [yes/no/CANCEL] no
vEdge1# conf t
Entering configuration mode terminal
vEdge1(config)# rollback configuration 2
vEdge1(config)# show configuration
vpn 2
router
ospf
no area 1
area 0
interface ge0/5
network point-to-point
exit
exit
!
!
interface ge0/5
no shutdown
!
no interface loopback2
!
vEdge1(config)#
