Topoprocessing is designed to support multiple correlations at the same time. But when we use the same name (type) of correlation in overlay topology request - we end up only with one such correlation received in TopologyRequestHandler.

Can be tested with following input:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<topology xmlns="urn:opendaylight:topology:correlation" xmlns:n="urn:TBD:params:xml:ns:yang:network-topology">
<n:topology-id>mytopo:1</n:topology-id>
<correlations>
<correlation>
<name>equality</name>
<correlation-item>node</correlation-item>
<equality>
<mapping>
<underlay-topology>mypcep:1</underlay-topology>
<target-field>network-topology-pcep:path-computation-client/network-topology-pcep:ip-address</target-field>
<aggregate-inside>false</aggregate-inside>
</mapping>
<mapping>
<underlay-topology>mypcep:2</underlay-topology>
<target-field>network-topology-pcep:path-computation-client/network-topology-pcep:ip-address</target-field>
<aggregate-inside>false</aggregate-inside>
</mapping>
</equality>
</correlation>
<correlation>
<name>equality</name>
<correlation-item>node</correlation-item>
<equality>
<mapping>
<underlay-topology>mypcep:3</underlay-topology>
<target-field>network-topology-pcep:path-computation-client/network-topology-pcep:ip-address</target-field>
<aggregate-inside>false</aggregate-inside>
</mapping>
<mapping>
<underlay-topology>mypcep:4</underlay-topology>
<target-field>network-topology-pcep:path-computation-client/network-topology-pcep:ip-address</target-field>
<aggregate-inside>false</aggregate-inside>
</mapping>
</equality>
</correlation>
</correlations>
</topology>