Mamiya 6 lenses

Hello, so I'm referring to lenses in the older Mamiya 6 folding cameras but may also apply elsewhere. I've noticed that some of the lenses are Sekor T, and some Sekor S. What's the difference in the S and T? Is it single vs triple coating?

At least my Sekor T looks like having modern multi layer coating.

Interesting. I'm pretty sure that's what the difference is, the whole Mamiya-6 timeline is really hard to follow.