Resolution:
No, it is not possible to retrieve the subject.

DATALOSS implies that we do not see the packet; it is based on a sequence number only.

All we have is a packet 'gap' and a source IP address.  There is no subject that we can use.

We assemble packets into messages, or strip messages out of packets.  Once we have *all* the packets for a message, we use a routine that retrieves the subject from the message.  If we miss packets, and we cannot recover them (due to data loss), we cannot know what the subjects were that relate to the data loss; we cannot even identify the sending transport (client), as the protocol is, by design, anonymous.  (If you want non-anonymous (identified) behaviour, you can use certified messaging, which identifies the transport (application endpoint) with a unique identifier.)