Hey Niels,
Thanks for your post! Let me try to answer your questions:
The matter with the IDs is admittedly a bit confusing, but traditionally the different authoring tools follow slightly different ways how to keep the components in a model identifiable. In principle, however, they all have a unique identifier system which helps to identify a component uniquely. These identifiers can be converted into each other and vice versa. E.g. Revit has the ElementId, which merely is converted into an IfcGuid when exported. As far as I know, there are also some plugins which can show you the IfcGuid in the Revit environment. So long story short, both values represent the same reference. If it didn’t do so, it wouldn’t be a unique identifier. For the BCF standard, the IfcGuid is decisive, which can also be seen here https://github.com/BuildingSMART/BCF-XML/tree/master/Documentation
Here are some blog entries by Jeremy Tammik on how to convert the Revit ElementId into the IfcGuid and back again.
http://thebuildingcoder.typepad.com/blog/2009/02/uniqueid-dwf-and-ifc-guid.html
http://thebuildingcoder.typepad.com/blog/2010/06/ifc-guid-algorithm-in-c.html
Solibri uses the IfcGuid for the identification. The reported entities option offers only the possibility to show other information in the presentation mode - this does not influence the identification system at all. Of course, the BATID should not change - and this is the same for the IfcGuid since it is derived from the BATID. If the uniformity of BATID and IfcGuid would change, then there is a massive error in the export routine!
As already outlined, the reported identities define which kind of information is shown in the error report, but it is not referring to the decisive reference within the BCF, so this will not change anything here. If a reference is lost, it means that the GUID of the element in the model was changed or broken, which might happen when remodeling, copying or doing a similar modification in between the versions. I would suggest, to compare the two versions of the IFC models with the Solibri Model Checker (Rule SOL/206) - with this you should get an overview of what has changed. Or search for the missing IfcGuid with a text editor. We could also have a look at this together in a web session. If you’re interested, please send a PM.
Kind regards
Cornelius