IFU-30 is the interface unit all by itself. The one with CD-ROM System written on it is the "combo" unit which included the interface unit + CDROM (IFU-30A and CDR-30A).
When the cdrom system was introduced for the PCE, the system was sold as two separate units. However, soon after (sometime in '89 I believe) NEC combined them into one package. Apparently the same CDROM drive was used in certain NEC computers so in theory all you needed was the interface unit in order to use it with the PCE.
I suspect that not many people had the CDROM drive by itself and since the PCE was a game system (sold in toy stores, etc) it was unlikely that people who bought the system even owned a computer let alone had the CDROM drive. But then again, you could buy the CDROM first and use it as a regular music player until you could afford the interface unit (which was more expensive than the drive).
Anyway, the separate packages were short lived but the prices were exactly the same if you bought them separate or bundled. However, I think only the IFU-30 by itself included System Card 1.0. The bundles had 2.0 or 2.1.