I believe entity types which predate R13 did not require or make use of the group 100 subclass markers, therefore (and per the documentation), for backwards compatibility, AutoCAD will ignore DXF group 100 for the following entities:
As such, entity types which do not feature in the above list will require the appropriate DXF group 100 subclass markers to be present in the DXF data supplied to the entmake/entmakex functions - it is also worth noting that since the entmake/entmakex functions are capable of generating non-graphical entities (e.g. Layers, Dictionaries etc.) both subclass markers are required because not all entities will derive from the AcDbEntity class.