I've encountered what I hope is a rarity, where a title has a different barcode printed on the slip-cover than the one on the cover-art of the keepcase itself.

The title I discovered it for happens to be 2 times present in the online database (once with one barcode and once with the other).
It's the movie 'Now You See Me' as distributed in Belgium:
8713045240165 - barcode on the slip-cover
8713045237721 - barcode on the case insert

Now I was wondering, which barcode has the preference to be entered in the database? I am assuming adding them both is not what should be done normally (as was apparently done for this title).
I would suggest adding the one on the slip-cover because that is the most likely one you scan to enter into your collection.

And secondly, this made me think more about slip-cover and cover-art handling. If a title has a slip-cover you can mark this with a checkbox, but does that marking have any bearing on the cover-art you are supposed to contribute? I mean, do you upload scans of the slip-cover or from the cover of the case (which sometimes is not the same)?

I would like to understand the best practice here.