Those Canon multicoated EOS lenses also have far more air to glass surfaces than the simpler LF lenses. The more air to glasses surfaces the more important coatings become and the more difference you will notice between quality of coatings.

I checked the serial number on my 203 Ektar once. That was back when I first got it in the 90s so memory may fail me but I seem to recall it was made in 1947. I've noticed no flare problems from it.