I enjoy collecting error cards but I have hesitated to buy any of the Nidoran 
or Nidoran 
cards (as well as any Nidorino/Nidorina cards). I wasn’t convinced at first that is was an error but the 3 latest versions of Nidoran:male_sign: (Steam Siege, Evolutions, Team Up) do not have a space.
I have been using TCGPlayer to quickly look through the card images.
I am curious was others think.
The proper spelling of the name is without a space so technically the ones with a space are “errors”. They won’t be recognized as genuine error cards unless they switched from using a space to not using one for the same actual card in an expansion.
@melchior, I guess it depends on what you consider an error. All Dark Arbok cards have the date of “1999-23000”, they were never corrected in the Team Rocket expansion. To me that is an error.
But I agree that the cards that get corrected in an expansion are usually lot cooler and worth more $$.
IMO if it never ends up getting corrected it’s not really an “interesting” error
In the end it all comes down to personal taste. Everybody is free to draw the line on what constitutes an error and collect them accordingly. To me, a simple space isn’t as interesting as the Dark Arbok example, for instance. Though both of them were not corrected.
I collect all errors cards, but one thing that is nice about error cards that aren’t corrected is that they are usually cheap and easy to find. And they are still fun to show off and talk about with friends.