The algorithm of which LISTSERV(R) hosts to use for any particular
distribution CAN be influenced by how many subscribers at a site (or
possibly domain) are receiving that particular item.  Say for sake of
argument, that one posting from a list with a specific topic is
distributed to two folks at your host, and another from the same list
with a different topic is sent to only one folk -- it is possible that
they will take a different Distribute path to your host.

Also, your personal SET options could likewise effect same if you were to
compare the path taken by two subscribers within the same host.

Finally, LISTSERV command responses (or posting ACKs) can travel a
different path yet.

Irregardless, multiple MX records could affect final delivery:

Query:Mail Exchange (MX):NBNET.NB.CA
NBNET.NB.CA     MX      10      smtp1.NBNET.NB.CA
NBNET.NB.CA     MX      20      smtp2.NBNET.NB.CA

assuming no inconsistencies in DNSes:

Query:Name Server (NS):NBNET.NB.CA
NBNET.NB.CA     NS      onyx.NBNET.NB.CA
NBNET.NB.CA     NS      dns1.sympatico.ca
NBNET.NB.CA     NS      opal.NBNET.NB.CA