so this is not a new issue... it was raised when the catalog was first incorporated into KStars. I've asked Christian to share his opinion.

Did Christian answer? I learned meanwhile that it is historically not clear, whether NGC5866 is really the M102 from Messier's catalog.

Afaik M 101 vs M 102 is a bit unclear in the reference databases. As I'm just converting OpenNGC to KStars ngcic format without changing existing entries, the proper place for that question is OpenNGC project: https://github.com/mattiaverga/OpenNGC

@cdersch: when I understand OpenNGC right, then they do not contain any Messier names. Where do they come from?

Messier cross-references are part of OpenNGC: https://github.com/mattiaverga/OpenNGC/blob/master/NGC_guide.txt#L60

Thanks, understood. But where does the M102 entry for N5457 come from? In the OpenNGC catalog it's only mentioned in the comment. Same for N5866, by the way.

Any consensuses yet on this?

Ok, it appears there is more weight now that is it indeed NGC5866. So that settles it for the time being.