+0
Please answer each one for me. Do you agree with my preferences. I highlighted them in blue font. Thanks.

Plurals of cap. letters
This one? A's, B's, C's, and D's
Or this one? A's, B's, C's, and D's (Italicize the uppercase letters, but not the apostrophe + s.)
As, Bs, and Cs look horrible because "As" looks like the word "as." Agreed?
I think that the straight type (in this example) for A's, B's, C's, and D's look best. Do not italicize the letters.

Plurals of lowercase letters
His lowercase a's and b's look horrible. Correct? I believe this is definitely correct.

Plurals of numbers
His 8's and 9's are not legible. I believe this is correct. Do not italicize the numbers.

His 8's and 9's are not legible. (italicize the individual numbers but not the apostrophe + s.)
747s or 747's?

Plurals of multiple letters
1 or 2?

RNs, DVDs, CDs, HMOs, RBIs I believe this is correct.
RN's, DVD's, CD's, HMO's, RBI's

Decades
1990s or 1990's? My preference is the one in blue font.

'80s or '80's? Same.

Thanks.
Comments  
Anybody agree with this?
Does this answer your questions, Vico?

Rule 11. The plurals for capital letters and numbers used as nouns are not formed with apostrophes.


Examples:

She consulted with three M.D.s.
BUT
She went to three M.D.s' offices.
The apostrophe is needed here to show plural possessive.
She learned her ABCs.
the 1990s not the 1990's
the '90s or the mid-'70s not the '90's or the mid-'70's


She learned her times tables for 6s and 7s.
Exception:Use apostrophes with capital letters and numbers when the meaning would be unclear otherwise.
Examples:Please dot your i's.
You don't mean is.
Ted couldn't distinguish between his 6's and 0's.
You need to use the apostrophe to indicate the plural of zero or it will look like the word Os. To be consistent within a sentence, you would also use the apostrophe to indicate the plural of 6's.