I ve checked around and the book seems correct See in particular the pages on NGC6882 and NGC6885 To be honest though I m not that fussed I think we could just word it as a possible duplication in the NGC and reference the discrepancies in SIMBAD and NGCIC org The text in O Meara basically discusses the fact different sources name this patch of sky differently which just leads to confusion about the ID In the book he cites several sources which label it as 6885 and several that cite it as 6882 I ll add the citations when your finished I think your right about the Rosette Nebula the fact is there are a string of NGC i d s for the different parts and some users just quote some of them is neither here nor there