For old cards that have been printed with the same functional abilities, but with a minor change, can you use the old cards as the new ones? For example, the new Shadow has no limit to the number of them in your deck. Have the old Shadows been errated to include this text? Same goes for Sea Neon, and maybe some other cards that I'm not aware of.
Additionally or alternatively, is there anywhere you can find a comprehensive list of errata for cards?