Lee registers off the case holder, which is also the base of the case, not the inside of the "inside of the cartridge base".The Lee trimmer sets the length of the cut from the inside of the cartridge base. That distance changes depending on lot number, manufacturer and wear. The "lathe" type trimmers are set to give true dimensions from the base of the cartridge to the mouth of the case. This means that the cases, regardless of internal dimensions, will all be the same length every time. That is the biggest advantage to the "lathe" type of trimmer. The trimmers with a single "universal" shell holder offer another advantage, if you want to take advantage of it. Since the "universal" shell holder places the base of the case against a fixed block you can make bushings to fit the different cases that you have after setting the trimmer up for the shortest case you load for. This is what I did and I no longer have to readjust the trimmer when I change the cartridge I am trimming. I just swap in the correct bushing and trim. All my cases are uniform in length without ever having to adjust the trimmer.
I am a fan of the WFT2..............I like it better than the Wilson/Sinclair that i sold after buying setting up and using the WFT2.Take a look at Little Crow Gunwords Worlds Finest Case Trimmer.
https://littlecrowgunworks.com/product-category/case-trimmers-and-case-prep-tools/?v=7516fd43adaa
It passes through the flash hole and stops against the shell holder. The base of the case is in contact with the shell holder. Therefore the cutting stops when the pin reaches the bottom of the case. Same as L.E. Wilson's register off the bottom of the case.Doesn't the case length gauge have a pin the goes through the flash hole? What is it that the pin hits to keep it off the inside of the case?
You are educating me here because I stopped using Lee products a long time ago.