Folks, I am going to toss my own opinion in here, though please understand that I qualify my advice as I have not tried myself to code "off brand" lenses.
Personally, I would recommend not coding them at all. Those codes were designed to correct individual lens characteristics in the specific Leica lenses they are assigned to. And more than just those pertaining to the focal length. I would suggest for your consideration that any software compensation due to reading the code is going to adjust your image file in a manner that will only serve to over-correct and distort your image when used on another lens. These codes were developed specifically to "tune" the final image file a specific direction. There is no way a Zeiss lens is going to need exactly the same corrections that a Leica 21mm will need. I point out to you that there are at least two 21mm lens codes. Ask yourself why. Because the Leica engineers found that there was enough of a difference in the two lenses that they needed to have two codes. And no code whatever for my most loved 21mm f3.4 SA. Any correction I feel is needed to the image files from my SA I do myself in my post processing programs.
Rant switch on :lecture: My second objection to doing this is an artistic one. Who among us as artists want to see final prints that all have the same look, coming from many different photographic artists? If I pick up another magazine, and stare at the cover image thinking "Yep, another 1DsIII photo" I think I am going to scream.:cussing: Everyone shooting the exact same camera, with the same lens selection, results in everybody having pretty much the same lens signature look to the whole bloody world's body of work from this period of time. :sleep006:
Why do I prefer using the older Leica glass, for the most part? Because they ARE different, each with it's unique drawing, contrast, flare, flaws, color shifts, IR bleed, and blacks that turn the whole world purple, in just the perfect light. For myself, as an artist the M8 is the perfect artistic tool, warts and all. Heck, the warts are what makes it challenging for me. What can I create using a lens that is almost as old as I am? Yea, I could code it and yes, that too would be yet another distorted view of reality, another artistic tool. But I think the engineers at Leica have done a magnificent job of designing these artistic tools just they way they are. I think they are pretty well perfect, just as they are intended to be right now. Who am I to argue with perfection? :lecture: Rant Switch Off. Just my own opinion, your own may vary. But for me, I have no interest in even trying to make my 21mm f/3.4 SA look like a 21mm ASPH. I Love it just the way it is .... warts and all.