Some natives say that they are not always sure as well.
***** NOT A TEACHER *****
So true, Tedwonny.
Here is an example that drives me crazy:
Visitor: I have some questions about this place.
Employee: No problem, sir. The _____ center is on the second floor. They will be happy to help you with any questions.
I have seen it spelled as:
1.
visitors'
2.
visitor's
3.
visitors
4.
visitor
*****
a. According to the traditional rules, the "correct" answer is #1. A center for visitor
s.
b. Some people think that it means a center to help any visitor. Thus, #2.
c. Americans do not like unnecessary apostrophes. So they simply drop the apostrophe as unnecessary. Thus, #3. (I admit that it does look cleaner that way, don't you?)
d. And #4 shows that some people feel there is no need for an unnecessary "s." So they simply use the word "visitor" as an adjective.
*****
It appears that the "rule" is: the particular business, organization, publication, etc. decides how it wants to spell its name.
By the way, maybe "Reader's Digest" is more personal than "Readers' Digest." That is, "Reader's Digest" might imply something like: this is a digest of interesting articles for a reader like you; "Readers' Digest" [the so-called "correct" form] might be considered less personal.
James
P.S. I do think, however, that most teachers would be upset if you wrote "boy's restroom" [toilet] instead of the "boys' restroom," but I suspect that most people would simply write it as the "boys restroom."