There is definitely variation among the various serial numbers of 50mm f1.4 lenses.
The earliest serials, say starting at 100,000-200,000, had a yellowish coating. These were the so-called silver nose. Some have said that they used thorium glass but I have not had a confirmation of this.
I have a 5xx,000 serial number that is more clear than the earlier model. But the coating is still a yellowish color. I am not sure if it is MC or not. But when I put it right next to a MC-labeled serial number 8xx,000 lens, it looks different. the later model lens has more of a purplish coating, and appear to have better coating, as the reflections are darker and I can see into the lens easier.
I dont have a f1.4 over serial number 1,000,000 so i cannot comment.
So I can honestly say that the later serial numbers of this lens have better coatings, but I am not sure if the design changed.
here is a good website to reference:
http://www.datasync.com/~farrar/zuiko.html#normal