When you are creating labels in the Web Service plug-in, in order to make available response data to the rest of the request, your response may contain multiple elements with the same name or path. If you want to be able to assign a unique label to each element, use XPath indexing, as follows:
ServiceName_1 /soap:Envelope/soap:Body/ns2:requestDetailResponse/service/serviceName[0]
ServiceName_2 /soap:Envelope/soap:Body/ns2:requestDetailResponse/service/serviceName[1]
ServiceName_3 /soap:Envelope/soap:Body/ns2:requestDetailResponse/service/serviceName[2]