No, there is no other documentation available for the details of the data collected by the unix and linux add-on.
Meaning of each field for the sourcetype protocol is as below
IPdropped - Outgoing packets dropped
TCPrexmits - Segments retransmitted
TCPreorder - Detected reordering
TCPpktRecv - Segments received
TCPpktSent - Segments send out
UDPpktLost - UDP Packet receive errors
UDPunkPort - UDP Packets to unknown port received
UDPpktRecv - UDP Packets received
UDPpktSent - UDP Packets Sent
If you want to understand the meaning of fields for other sourcetypes, like SloshBurch said you will have to understand the script of that sourcetype.
And for the data collection of the packets re-transmitted, as per my knowledge only TCPrexmits field of sourcetype protocol contains that data.
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