Hi T0r. Yep, I can see where that would be an issue. If you're referring to that specific coin (the one that received the "Shipwreck Effect" designation), there is a workaround I've discovered in order to get the hyperlink to work correctly on Numista for the time being.
For those coins, NGC intentionally does not straight grade them. If you just plug in a random grade (say, “MS 60”) for that one and then complete the process, the hyperlink will work correctly on Numista. I just added it under my own collection as a test and got it to work that way. Yes, it's a little cumbersome. Numista would have to create a generic plug value for the “Shipwreck Effect”, and then add “Shipwreck Effect” itself as an additional designation since NGC intentionally doesn't straight grade those coins on purpose. I hope this makes sense.
NGCX slabs are a different matter, and I totally forgot about those. Yep, Numista would have to add a new Grading entry to accommodate those.