I thought of this question while reading Why are there illegal cards?, which mentions that the illegal Egyptian God cards were later printed as legal versions with the same names.
In Magic, all tournament-legal printings (non-tournament-legal ones would be, for example, promotional versions with different card backs) can be used as the up-to-date card. An old card functions identically to a new card of the same new, even if it was originally printed with rules or wording that don't work anymore.
Does such a rule exist in Yu-Gi-Oh!, or are cards as-printed? For example, can the illegal Egyptian God cards (e.g. the original Slifer the Sky Dragon) be used as their updated legal versions (e.g. the updated Slifer the Sky Dragon)? If not, have the rules been maintained in such a way to keep older printings valid?