The other problem with these "copyright traps" is that they do nothing to prove someone copied the
legitimate parts of the data.
Suppose you recreate the entire dataset from scratch. Then someone notices (e.g. using an automated comparison) that the "trap" is in the other dataset but missing from yours, and submits it to you to add.
This is arguably too small an addition to be copyrighted on its own, but regardless of that, it would then be all you have to remove to get back to a clean version. And since it's erroneous data, you would want to remove it anyway.
