I noticed that the Nintendo 64 Modem was recently added to the N64 dat. There was an internal discussion whether the ROM belong to the N64 or the 64DD-dat. I quote from the previous discussion.
einstein95 wrote: ↑13 Aug 2016 16:25
Asked luigiblood:
[03:23:12] <> It came with the 64DD since it normally comes with Randnet
[03:23:42] <> It's a cartridge that cannot be booted
[03:24:39] <> lack of CIC
So it'd be a definite 64DD considering that all other N64 files in the dat can be booted.
I remember why I never got around to add it to the dat. I couldn't determine whether it was an overdump or the physical ROM size really is 8MB.
"The ROM is 4MB, but mirrored to 8MB: one copy at 0x18000000, and another at 0x18400000"