One problem is they are official site reviews. The site can't really have two different official reviews*, which is partly why I now regret us doing new reviews for Director's Cut versions of what were still very new games.
An extension of that is it also poses this question: which review becomes the site's official review on aggregate sites? The first one, or the second one, and why?
While I certainly see merit in an updated look at a game that may have been patched extensively and given significant free content updates (I'm thinking something like No Man's Sky, which by most accounts is now a radically different and much better game), I think this is more appropriately covered in an article rather than a second scored review that in a way overwrites/overrides the original.
*(I will say I do like the Famitsu approach of having 4 individual writers giving their scores, which are then added together to give a combined Famitsu total, but that's not feasible for any but the biggest outlets. It's also slightly different in that the separate reviews/scores are all done at the same time and it's baked into their system from the start, rather than being haphazard after the fact.)
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