The following returns an empty array:

var sdnoRow = sdnoColumn.Lookup(channel.Label);

However, the following returns true:

sdnoColumn.GetValue("31793.0.31794").Equals(channel.Label)

Have I misunderstood what Lookup() is supposed to do?

EDIT: More context added

var dms = protocol.GetDms();
var sdnoV2 = dms.GetElement(new DmsElementId(127701, 250));
var sdnoDestinationsTable = sdnoV2.GetTable(1300);
IDmsColumn<string> sdnoColumn = sdnoDestinationsTable.GetColumn<string>(1302);

foreach (var channel in channels)
{
var sdnoRow = sdnoColumn.Lookup(channel.Label);
...
}

I ended up using IDmsTable.QueryData() instead.