Probably because the artist added it to SC on May 1st, but made it public (ie., released it) on May 28th.
Is this an actual video? If so, it should be added as its own standalone recording.
Ideally I guess we should have both May 28th and 31st as release dates, but we can only have one date per country/region, so I'd just go with earliest. If you care enough, you can jump through some hoops and set dates on the URL relationships (and/or just note this in the annotation).