Hi,
In addtion to Surya's post, I just try to clarify the rib-group function.
There are two entities here. One is "Routing Process/Protocols" and the other one is "Routing Table".
RIB Groups and import/Export polices interacts between these two sets of entities.
If you take rib-group,
import-rib -- > Installs routes from a routing process to one / many routing tables mentioned in the group.
export-rib --> Exports routes from a single routing table to protocol.
So in your case, routes were installed to vpnA and vpnAB routing tables from BGP.
But you can't expect routes from vpnAB table will be installed to vpnA / vpnB table. ( This is not between protocol and table)
This will happen when only vpnAB BGP installs any routes to vpnAB table.
Regards,
Moses N