With regard to the downloads. I'm afraid what is linked on the website is what I have. I don't have any other versions hidden away anywhere. I moved the whole site to a new server about 10 years ago and most of it hasn't changed since. If there are other versions floating around later than 4.00.23 then they must be earlier beta versions.
I didn't do any special custom versions for anyone so any differences in the ones you are finding are down to either them simply being from a different period or perhaps, as you suggest, the post-processing involved in creating elevated or signed executables.
In TGATool2 in About>DLLs it says that mwtwack.dll is missing but I couldn't find it in the latest version which brings mwgfxdll.exe. What about this file?
In the early days of mwgfx some things were initially provided by extra dlls that were later incorporated into the main dll set
mwtwack is actually an interface to the windows Twain system which controls imaging devices such as scanners and cameras. It provides functions to select and operate twain devices and import images from them. The strange name is actually from windows which calls an object accessing Twain functions a Twacker.
The twain code was long ago incorporated in to mwgfx24.dll so mwtwack.dll is no longer needed.