As with all oil related subjects. It can get confusing. It doesn't seem to be any different with the JASO ratings. Although this should not discourage the average consumer from grasping the very simple aspects of this very important rating that apply to their needs. Especially when the wrong JASO rated oil can end up costing a bundle to fix a destroyed clutch.
At the risk of making things worse, I will say that though you are correct, there is more than just a catalytic converter component difference between the various JASO ratings. You can see this by the chart below. Also, you will not find the different ratings normally listed in the order I use in my chart. MB, MA1, MA & MA2. I listed them this way because it seems more logical to me to list them from the least clutch friction offered to the most clutch friction offered. I think the reason JASO lists these in different order is that they are grouping the catalytic converter and the non-catalytic converter lubricants together. This is also logical in that respect.
It is my understanding that the MB and MA rated oils are not catalytic converter friendly. And that the MA1 and MA2 are. Interestingly enough. We are sacrificing additional engine wear to protect our catalytic converters. Everything in life is a trade-off. It is no different with lubrication.
The way this rating works is that all 3 components must fall within a rating to qualify. So, for example, if 2 components fall within the MA2 range, and 1 component falls within the MA range. That oil would receive a JASO rating of MA, not MA2.
You can click on the chart below to make it readable.
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