Civilizations come and go. The significance of recovered artifacts is not always fully understood but the recovered items are often recycled into the next version. And, in this case, possibly updated. A common theme throughout ancient empires. The cross is obviously a universal symbol.
Just as the Elephantine Island platform is not the original but has been remade, as best as the recyclers could, even using fluted columns as a pier foundation. The extreme example is the current restoration of the Sphinx using cement and bricks. It is to render the edifice as best as is practicable in a certain era to correspond with what the restorers assume that the original looked like.
So, with the nilometer. I have not claimed that all images which were presented are of the original item, but are presented as a comparative viewpoint. Please feel free to discard any or all examples, which you may feel are incongruent. I do this with posts whilst still being in agreement with the thrust of the main topic.
Again, thanks for the feedback.