Okay, I'm back (again). Using $sth->fetchrow_hashref seems to be solving my problem. I have discovered that one cannot use $sth->fetch if one chooses to execute a query containing conditionals based on fields; i.e.

$sth->prepare("SELECT * FROM db WHERE field < 2000");

while (@row = $sth->fetch) {
    ...
}
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will return the first row and then nothing beyond that. If I use

while ($row = $sth->fetchrow_hashref) { ...
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for some reason, everything seems to be hunky dory. Also, that "undef" in setting up the column names and variable references also is wont to cause me difficulty ("perldoc DBD::CSV" for reference on that one). Go figure.