Are the SKUs of an album on a label's online store the same as the album catalog number?

This question is about this release-group: Release group “Legacy of the Dark Lands” by Blind Guardian Twilight Orchestra - MusicBrainz

The group contains two albums with no barcode and an odd catalog number. and

A Google search shows that these were the SKUs of the albums in Nuclear Blast’s online store.

Are the catalog and SKU treated as the same or should the releases have their catalog removed and merged with the proper ones? and

No. SKUs are assigned by retailers, not labels. SKUs are unlikely to be printed on the release and are not equivalent to release catalog numbers.

That is what I thought based on my knowledge how how stores and SKUs work but I admit I have never bought a physical CD so I did not want to assume.