Exception: Use apostrophes with capital letters [sic—the first example uses a
lowercase letter] and numbers when the meaning would be unclear otherwise.
Use an apostrophe plus -s to form the plurals of letters, numbers, and
words named as words.
That sentence has too many but’s.
Remember to dot your i’s and cross your t’s, or your readers may not be
able to distinguish them from e’s and l’s.
At the end of each chapter the author had mysteriously written two 3′s and
two &’s.
[...]
Exception: References to the years in a decade are not underlined
[italicized] and often omit the apostrophe. Thus either 1960′s or 1960s is
acceptable as long as usage is consistent.
Correct or not, the style guide is lame. A clearly superior way to prevent the ambiguity with unfortunate clear default is to use single quotes on both side of the ‘i’. So ’i’s, not i’s.
Rule 11:
If you were looking at the link I posted before editing my comment, search for “tired” and “DO use the apostrophe to form the plural”.
My 1992 Little, Brown Handbook says:
Correct or not, the style guide is lame. A clearly superior way to prevent the ambiguity with unfortunate clear default is to use single quotes on both side of the ‘i’. So ’i’s, not i’s.
I’ve missed that, thanks.