How do I say it?

[The Radium King]

don't think the op was asking whether people would 'know' what you were talking about. he asked about 9-8-6 vs 9-86. valid question given the disparity in tradition throughout the years.

I think it has to do with how quick it is to say:

9-eleven faster than 9-one-one
9-nine-three faster than 9-ninety-three

9-eight-six faster than 9-eighty-six

same reason the French can't win a war - takes them too long to say 'duck!'.