unmkinitramfs in initramfs-tools-core doesn't fully extract an initrd in bionic

I am running Ubuntu 18.04.4

I am looking at the initrd found in the desktop live cd (<cd loop mount>/casper/initrd). If you execute `binwalk initrd`, binwalk informs that the initrd file contains 2 cpio archives and a lzma archive

The first cpio archive is supposed to contain kernel/x86/microcode/AuthenticAMD.bin
The second cpio archive is supposed to contain kernel/x86/microcode/GenuineIntel.bin
The third file is a LZMA compressed data

Now, if you execute `unmkinitramfs <cd loop mount>/casper/initrd new-directory` , you will see 2 directories, "early" and "main".

"early" has the AuthenticAMD.bin, which means it corresponds to the first cpio.
"main" is the actual initial ram disk file system, which comes from the LZMA compressed data.

What I expect to see is also the GenuineIntel.bin firmware. `binwalk` says it's there, but `unmkinitramfs` is not able to extract it out. Why?

I see binwalk is at version 2.1.1-16, while initramfs-tools-core (which provides unmkinitramfs) is at version 0.130ubuntu3.9.

How do I extract the ubuntu 18 initramfs and get all the contents that binwalk is able to see?