Hi,
I asked the same questions because I was as confused as you.
Basically, old part number inks for the 4800 will fit in the 4880, but will not work, because of the chip inside them, which won't recognise the 4880.
The new part number inks will work in both the 4800 and the 4880, with the exception of the vivid magentas.
I haven't tried any of this, but managed to glean this information from various sources on the web, including Epson themselves.
Hope this helps.