"AutoCAD Architecture is IFC-certified for importing and exporting version 2x3 IFC files. IFC files from versions 2x2 and 2x can also be imported if the data is compatible with 2x3 and is consistent with implementation agreements as defined for the IFC 2x3 coordination view. For more detailed information, go to http://www.iai-international.org and search for IfcWiki Web resource."
It appears that website has been re-purposed since 2009. I got a kick out of it.