In the past was duplicate used for posts that were uploaded first but later had a superior version uploaded? It seems like some wikis still reference that, but it's very clear now that that's not supposed to be the case:
This tag only applies to inferior posts that were uploaded after an already existing identical post.
Pixel-perfect duplicate seems to suggest that the post that was uploaded first can be tagged as a duplicate if it has no source:
A post that is completely identical to its parent down to the pixel and was either uploaded afterwards or has no source while their parent does
Bad id outright says this:
If the filesizes are different and the image is superior, then upload it if you consider the image worthy, then parent the original to the upload (by clicking edit on the child post and pasting in the parent ID in the parent field) and then tag the original upload with the duplicate tag.