Hello Zaman
Regular IP packets by definition do not have a label. They are always processed as regular IP packets based on destination IP and routing table lookup. So they are always routed using the FIB table. The LFIB table is only used when there is an MPLS label.
As for the untagged label, you can find out more about that at this post: Introduction to MPLS
I hope this has been helpful!
Laz