In an answer to this recent question there is a screenshot of a Cardassian who has been assimilated by the Borg. My question is simple: when the hell did the Borg come into contact with the Cardassians? According to every Star Trek map I have encountered, the Cardassian Union is on the opposite side of the Federation to Borg space, which would seem to preclude the Borg 'recruiting' while passing through on their way to assimilate Earth.
Is there any canon or non-canon material on how exactly the Borg came into contact with Cardassians?