AE/MM switch, theta compensation & no lugs on Yashica lenses

You'll probably get a mix of answers on MM tabs in general, with most of them being speculative. The only hard facts I can offer about the Multi Mode Zeiss lenses when used on Yashica branded bodies will be pretty basic and simple... they don't seem to matter to the camera if they're there or not. In practice, I'm not sure if every MM lens on every C/Y Yashica body would perform flawlessly despite the tabs being there or not. I don't recall seeing anything about them from 'official' sources that they'd fail or have issues on Yashica bodies, but that's not to say that didn't or couldn't happen.

I personally don't have a 109 or the TR, and the only 108 I have is an Oral Eye version so I have nothing to test with. I think the only way to know for sure what works and doesn't, is to try each camera individually, and not to assume the entire family models won't work because of some quirk. It also might come down to what physical limitation might be there to interfere with the tab itself too. If there's an obstruction, it might not even take the lens and/or lock it into the mount, so in those cases it would definitely rule out the entire model line.

For the Contax bodies that offer automation, they do rely on the tab's presence to work fully and 'as designed', and will impose some limitations when they're not present. The presumption (by me) is that Zeiss was hard-nosed about how beefy and over-engineered their fist line of C/Y products had to be, and that turned against them later on. Their heavy-duty approach ends up wreaking havoc when implementing any new program mode features. However... It's simple enough to fool any MM Contax body that it has an MM lens attached by sticking a small bit of plastic into the body slot to hold the switch in the MM position. Theoretically any lens with a C/Y mount can present itself as a Multi Mode lens. That's not something I've tried with absolutely every lens I own, but it does enable all the Tv and Av functions without complaint with those I've tried.

I have to assume that third party makers wanted access to the C/Y arena in every manner possible, and it might be that adding their own MM tabs was as much of a marketing stunt for some of them, than just a necessity. "Upgrade your Adaptall mounts now to get these new features...". Yashica may have also taken advantage of the Zeiss shortsightedness and thumbed their nose to making changes. They could point to their own compatible bodies as already being fully programmable for any/all Zeiss lenses since day 1. I wonder if there were mentions of it in the trade press at the time...?

The change to MM wasn't just for automation. They hid some optical upgrades to both glass and coatings in all but a couple of lenses, and they got rid of the 'ninja' bokeh bubbles too by getting new blade shapes.

For #'s 1 and 3...

1.) The newer MM-centric Contax bodies had much faster shutter speeds - up to 1/8000 - and may have had issues with blade shapes, friction/drag from materials and finishing methods or pivot points, and/or overall weight issues, in order to match the performance needed.
3.) I'm not sure if it was a significant factor, other than cosmetic appeal or maybe it was marketing trickery. I'd assume if it were somehow pertinent to MM functionality, there'd be some mention of it in documentation or sales info.

Since I'm not a programmed settings user either, that one eluded me, but makes perfect sense. That seems to make the markings coincidental in specifically using Contax MM tabbed lenses, and simply a requirement for using Yashica's automation with any C/Y lens used... Zeiss or otherwise.

Thanks, everyone, for the well-reasoned explanations!