When transaction IDs are used and data is import into SiteCatalyst, you
cannot change any values assigned to a transaction once a value has
already been provided in the past. If you were to upload new values for
a transaction ID that already has values assigned to it, you will simply
append the data to existing data for that particular transaction ID.
This creates a double count effect. It would be nice to have a feature
that would allow us to automatically overwrite the value currently