@Clarity Finally some progress...and some failures.
But let's start from the beginning of my adventure.
1) The trigger
I saw your post here . Because it promised a small download, I decided to go for it. I'm using Slacko 5.6 on a 2GB Netbook.
Downloaded SG2Dwith2PUPs.img.zip and unzipped, but I didn't know what to do with it.
2) Hunting for info
In your opening post I found, as kind of side note "You will notice, too, on the download site that there is a "README..." of known utilities that will create a USB from an image file" . OK, finally a hint on how to create such device. Next stop your Google Drive - again.
Found 2 READMEs in DOCX format and a script FlashImage2USB.sh. Downloaded all 3.
What I don't understand here: Why 2 READMEs when 1 would suffice? Why DOCX and why on the Google Drive at all? It's not that much information and it would make a perfect forum post. Please consider to make this important information easier to access for casual users like me.
3) The acid test
Tried the FlashImage2USB.sh script. The code starts with "# CREDIT: Prepare and submitted by BigPUP on the Puppy Linux Forum" Couldn't find anything "on the Puppy Linux Forum", not the new one, not the old one. Maybe @bigpup can help?
Anyway, the script didn't work for me - and so did your code examples in your READMEs. The problem is the status=progress
argument, which is not supported in my version of dd. BK mentioned this in his blog post and wrote that he had solved the issue in his easydd . Maybe, as a general rule, it would help if you also test your tools on older Puppies to find any incompatibilities. Even such stone age tools like dd may contain surprises 
With a reduced dd command I achieved what you saw in my previous post. I tried to mount the resulting mess with pmount. Pmount froze and I had to kill it.
4) Testing on a different computer
I removed the stick from my Netbook and tried to boot with it on my desktop PC (sporting an old AMD Athlon 64x2 Dual Core Processor 4200+ with 2GB RAM). Nothing: "This is not a bootable disk. Please insert a bootable floppy ...". Good joke. In the BIOS the stick didn't even show up, so couldn't prioritize it in the boot order. Back to the Netbook ...
5) Second attempt
Inserted the stick and - tadaaaaa!! - both partitions appeared as icons and could be mounted. Gparted showed no problems:

- screen_2022-12-02_11crop.png (29.34 KiB) Viewed 3131 times
Seems that all I should have been done is remove and reinsert the stick.
I expanded the 2nd partition with Gparted, added 2 ISOs (tahr-6.0.6-uefi.iso and xenialpup-7.5-uefi.iso) to /BOOTISOS and booted. Being on a 32bit machine I booted Slacko7.0 - and it worked.
Great!
The problem: the 2 ISOs I added didn't show up in the menu. The menu says that it looked into /boot-isos and /boot/boot-isos, both directories that don't exist in your setup Why does it find your 2 ISOs in /BOOTISOS but not mine?
So as of today I have a stick that works on *some* computers and doesn't accept new ISOs.
I also don't understand the choice of NTFS as file system. To make it MS Windows compatible? Just a mistake? In your opening post you claim that your IMG files are formatted as EXT2 or F2FS (BTW: Adding the information which of the files is formatted as what would be helpful)
Anyway, interesting stuff
Thank you!