At Y!A I have answered more than 200 questions, with a "best answer rate" of 6%, so should have 12 "best answers".?

This is all your 12 Best Answers. https://ca.answers.yahoo.com/activity/answers?view...

You can see them any time by clicking your avatar and then Best answers.

You can click Notifications on the left side of any page and you will get a notice there too.

/notifications

Your latest Best Answer was on a question where your answer was posted just 23 hours ago, here:'

/question/index?qid=20141...

You should be getting emails about these. Check your SPAM folder, as you may have accidentally marked one as spam at one point, which might be causing this issue. You can always check for yourself, by coming to the site and clicking your nickname or avatar on any question or answer you post, or at the top LEFT of the page where they show under the Notifications link.

I have never received an email advice about being awarded even one!

It's not that I do it for that reason, but I like to know which of my answers people are finding helpful, and had received no comments for several months, so I can only assume that they were discontinued.

I have just checked your profile page - you have answered 205 questions, and do indeed have 12 best answers.