When using the snapshot version, can I assume that it is at least the latest version, in this case, 23.05.2 which may or would become another higher version later?
I'm using snapshot but I can't seem to find any info on what version that actually is.
Nope, here's a picture of how versions work (scroll all the way down to the "Branch logic" section):
Basically, what we call "23.05.2" is actually a branch off the main development branch, and has its own history separate from the snapshot branch. Of course, some stuff like bug fixes in snapshot gets merged back into the 23.05 branch, but all the new features (such as new device support) happens on snapshot.
No, the snapshot releases are built from the current main branch and have many, many (many!) changes since 23.05 was released.
You can look at https://git.openwrt.org/openwrt/openwrt.git for what's on main, and down on the bottom of that page, you can get to the 23.05 tree via the link under "heads".
Care to elaborate a bit on the nature of this custom software package? Does it depends on specific kernel modules (which does get affected by snapshot versions)?