Apostophes are the most misused of punctuation marks. How many times have I wanted to take my red pencil to a sign reading "Mens' and Womens Restroom's" Agghrrrrhh! Or "We sell CD's and DVD's" or even, "He was raised in the 1960's" [I'm fighting a loosing battle on that one, I have to admit.]
Generally, the apostrophe is used to represent letters left out (Rock 'n' Roll; can't; the '60s); or to show possessives, and never to show plurals.
But, for the plurals of single letters and numbers, the apostrophe is required for clarity's sake.
The Oakland A's is a sports team. Be sure to dot your i's and cross your t's. I deleted all the 9's from your list.
It is also acceptable to use it, if you are 100% consistent in the same text, to avoid confusion with other words. For example, if you are writing a book on deer or rabbit raising, you may wish to comment in the foreward that you know how to spell the plural of doe, but just for the sake of easier reading, you are going to spell it as "doe's". That way, it doesn't screw up the reader with does (rhyming with duzz) vs does (rhyming with toes).
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