Problem solved. I'll explain after this public service announcement: Do not, I repeat, DO NOT follow the instructions in my Sept. 3 message. I made two serious mistakes: First, I thought that the newly created Search Folders contained copies of emails in my systems. Oh, no. The Search Folders are just a different view of the same emails, so when I deleted messages that were outside my search parameters -- and emptied the deleted messages bin -- I essentially wiped out my historical emails. My second serious mistake was assuming that I could just retrieve my deleted emails from the O365 cloud.

Fortunately for me, my laptop was turned off while I was doing all of the above on my PC. With the able assistance of Microsoft's support organization, I was able to restore all (I think) of my historical emails.

O365 does not include backup/recovery services. Yes, a copy of your email is stored in the cloud, but it isn't there forever. I thought it was stored for the duration of my subscription. Bad planning on my part.

And now, the solution to my original post about how to create a particular customized search in Outlook 2013. I wanted the ability to identify all emails sent and received in a given period of time, and to be able to sort those emails by folder and subfolder. I tried using the "between" two dates option, but could not get the protocol right for the dates. Here's the solution:

In Outlook 2013:
1. right-click on Search Folders, then click on New Search Folder.
2. in Select a Search Folder, scroll down and click Create a custom Search Folder.
3. click Choose; input a name for the new search folder then click Criteria.
4. after you click Criteria, click Advanced/Field/Date-Time Fields/Received.
5. under Condition, scroll down to Between and click.
6. under "Value", insert two dates using the following protocol xx/xx/xxxx and
xx/xx/xxxx, then click Add to List.

This will search for all emails Received between the two dates. To also include all emails Sent between those dates, click Field and follow steps 4-6 above (except replace Received with Sent in step 4).

The result is a search folder that shows all emails sent and received between two dates, with the ability to sort by folder and subfolder. I created search folders for each month of 2015 so that I can confirm the transaction-related parts of my invoices before I send them to clients.

This is an invaluable feature to me. I hope that others find it helpful... and learn from my multiple mistakes.