As a suggestion for your testing: if you make volumes instead of partitions you can add and delete OSes much more quickly, and without resizing your existing volume. This is how Apple recommends doing it.
Use more than one version of macOS on Mac - Apple Support
Thanks, yes misspoke. Old habit to say partition but meant the APFS volume. Really do like this feature.
For whatever reason, erasing the volume, reinstalling ventura from recovery, and then upgrading to an earlier sonoma release did not fly. After opening, it was at 14.3.1. I intended to install 14.1.2 using the specific installer noted above.
Not sure if macos didn't like two different sonoma releases on the same container or if the installer just didn't take, but re-downloaded 14.1.2 again, erased the whole machine and started fresh with a clean ventura install, and THEN installed 14.1.2 no problem.
Good thing is, this release is good enough for my workflow (although ventura surprisingly is the best). It was some trial and error as everything released after was a problem. Now at least I know.
Appreciate the good tips in this thread. It took some time today, but it all worked out. Even was able to migrate from my old machine with 14.3.1 to the new machine with 14.1.2 with only a few hiccups.