I wonder if there's a 'canary' post code in this data that doesn't actually exist but could be used to prove where you got the data from. That's the sort of thing I'd do.
Anybody have any good examples they've seen on the computer side?
Unless somebody thinks this was a deliberate leak to poison the free data - in which case it would have it's own canary address
I realize that, but won't adding a 'bad' postal code possibly interfere with customers' usage of the data in the first place?
If they decided to post a letter to every address in the database then one of them would be undelivered - but that is probably not a problem given the efficency of the post service!