The 401 was their premium receiver of its day, and first Navigo (new one board reduced chip design, with tone generator built in and stacked certification).
It had full front buttons, support for the UHF remote kit, dual A/V out, S-video, digital audio, and serial port for HD decoder. Those were initially released middle 2000 or so.
The 301 (my first) was the basic receiver until the 2xx series boxes. It has only a power button/satellite indicator on the front, one row of composite A/V on the rear, plus RF modulator in/out, satellite in, modem. It is basically a stripped down 401. The 305 succeeded it. I would say they were released late 2000/early 2001.
The 405 is just an update of the 401, to go black, and use the new crop of parts as used in the 205 and 315. The 315 is an update of the 305, 205 a miniaturization of the 315 for basic TVs. The 405 was released 2004 or so.