MPLS VRF names locally significant
VRF names are locally significant and are not sent in any updates to other PEs. The RD is used to make an update unique within the MP-BGP portion of your MPLS VPN network and is sent as part of the MP-BGP update between PEs. It is what makes a prefix a VPNv4 prefix and not an IPv4 prefix. Therefore it needs to be unique within the network. Otherwise if the same RD is used on multiple VRFs for different customers there may be overlapping prefixes in the network.