I promised to stop the spam, but I have to answer your questions/remarks:
Let me guess...you must also think that in response to question B.8.a, it's necessary to list Costco/Sam's Club/local book club/PTA/etc. memberships?
No, I personally do not think that USCIS cares about those memberships and I did not report them on my own N-400. But I understand if people want to write those memberships down to have peace of mind and I saw on many forums that a fair amount of applicants prefer to list those memberships. USCIS will not deny your application because you listed your Sam's Club or AAA membership, so no harm with this.
According to an attorney's response to a question regarding approximate travel dates, it's acceptable to "give approximations if that is the only way you can fill out the form":
http://www.justanswer.com/immigration-law/1fdmo-hi-currently-filling-form-n-400-become-citizen.html
This answer was regarding travel dates, something far more important than employment dates. A simple Google search will return many immigration sites/forums where it's clearly stated by many individuals who have undergone the naturalization process that month/year is perfectly acceptable for the employment history field.
Agree with you on this one. If you are totally not able to get the exact date information, you put an approximate date.
But you try first to get the exact information, that's my philosophy. Some people suggest to put an extra sheet to the N-400 explaining that you put in an approximate date because you could not find the exact date. The same applies for employment dates. You give a call to HR of your ex-company and try to get the information. If you get it, you put the exact date. If HR is not able to provide you the info or you cannot reach them, you put in your best guess. You have peace of mind, and if the issue comes up during the interview (however small that likelihood is), you can say with a straight face that you tried your best to get the info from HR.
With regards to me not having a look at the N-400, take a look at my signature. I have successfully undergone the naturalization process, listing my employment dates in month/year format.
I meant that you most likely did not have a look at it lately. I clearly saw that you went through the N-400 process; I just wanted to point out that the date format issue is not in the auto-fill fields of the PDF. In all questions regarding dates, the format is given in MM/DD/YYYY on the N-400 form itself. So even if you take a print-out and fill in the form by hand, if you read the questions regarding dates, you will see that they want the MM/DD/YYYY format.
As a summary of this long thread, my two cents regarding exact dates is to try to obtain them from HR. Just give them a call. If you fail to reach them or HR is not giving you the dates for whatever reason, fill in your best guess. You will have peace of mind that you tried to get all the exact info and you can answer with a straight face and truthfully if anything is asked about this during your interview.