Valuable error cards are usually not one-offs like this one. When one card is different, it's usually considered damaged; when a certain amount of cards are printed with an error (usually a typographical error), it's considered a "run" of error cards. Take for example the base set cards that had the HP printed incorrectly. There was a specific run of cards where some of the pokemon had the error, and it was later corrected.
There simply isn't much of a market for individual cards damaged in printing. Valuing it would just be putting it out there and seeing who might be interested in it and what they offer.