How to obtain most universal macOS High Sierra installer / complete USB installer thumb drive?

[organicCPU]

This is a question to other macOS collectors.

So far I was able to cherish an operating system archive. My backup strategy usually consists at least of:
1.) a freshly from the MAS downloaded zip compressed macOS Installer app, stored on an external disk drive
2.) an installer thumb drive for later use.

With macOS High Sierra 10.13.x and the soon to be released macOS Mojave, I've got the feeling that I'll miss some important piece of installer for my Mac OS, Mac OS X, macOS collection...
In detail, I'm talking of Firmware updates for older Macs and special builds for newer Macs.

- I've been downloading the full size 5,23 GB installer for macOS High Sierra, version 13.6.02, from a newer Mac running macOS Sierra.
- I've been downloading a 22 MB sized installer stub from an older Mac running Mac OS X Mountain Lion.

So far I couldn't manage to download the full build 17G2208 for the 2018 MacBook Pro. I tried from macOS Sierra with the help of installinstallmacos.py from munki/macadmin-scripts github page. I didn't try from a VM running High Sierra with HFS+, but I guess, chances are better anyway getting that build from High Sierra with APFS, right?
Additionally I don't know, if I'll miss some model specific Firmware updates for mac OS High Sierra. Finally I've no clue, how I could make a working thumb drive installer with everything included and combined.

@SteveJobzniak pointed out in this thread https://forums.macrumors.com/threads/warning-do-not-install-high-sierra-from-usb-1st-time.2116175/ that there were problems with USB thumb drives not containing Firmware updates.

What are your strategies to obtain a most complete macOS High Sierra installer, before it'll be too late?

 

[Fishrrman]

I don't have a 2018 MacBook Pro so I can't address the specific OS issues that are related to it.

But...

The best way to get "the last, best copy of High Sierra" is to "re-download" it from Apple.
The installer you get should be able to install a fresh copy of 10.13.6 (fully updated)*.
Then archive a copy of the installer.
Perhaps create a bootable USB flashdrive version as well.

*Again, I don't know if this addresses the "special release" of 10.13.6 that was particular to the 2018 MBPro.

IF the copy on Apple's software download page IS NOT one that will currently boot a 2018 MBPro, I'm thinking that it will eventually be updated to become capable of that...

 

[organicCPU]

Thank you @Fishrrman for the reminder to re-download. I did that immediately. The new macOS 10.13.6 installer is the same as the one I've been downloading two month ago. Of course, I'll create a bootable flash drive with the final release ;-)

I don't have access to a 2018 MacBook Pro, either. I don't think that the special 2018 MBP High Sierra installer is at this time incorporated in the common MAS installer, at least not in the version that I can download with a 2015 MBP running Sierra. Nevertheless, I think it's nice to have that special 2018 MBP build available offline, too. Just in case, I'd ever need it later on and don't have an internet connection ready for a macOS Recovery over internet for the preinstalled macOS. If it's really impossible to obtain that build from a different machine, I'll need to accept it. However, if someone managed to regardless download it (e.g. with installinstallmacos.py on an APFS file system), I'd be glad for hints to have a more complete macOS installer library.

The second part of my question is confusing me a little more. So far, I never had these thoughts on previous installer thumb drives, but the current High Sierra installer is making me slightly nuts. I'm asking, because I don't want to trigger an unneeded firmware update right now, just to test if the installer drive would work. Other users have reported that a full macOS High Sierra installer USB fails to install on older Macs, exactly on those that need Firmware updates before. Is that still the case or am I worrying without any reason?