Pretty serious issue related to searching emails

Pretty serious issue related to searching emails

...Frankly...I hope this has not been occurring previously or there may be many many emails I have missed....I hope I am just discovering this now because it is just NOW happening.  Here is the situation:

When I go back to organize my emails, I will do a search which is like the following:

Sender = bruce or Sender = adam or Sender = craig or Sender = eric or Sender = heather or To = bruce or To = adam or To = craig or To = eric or To = heather

and then in the additional options, I will set a specific date period, i.e. 2/21/2014 - 3/20/2014.

I then get a bunch of emails responding to my search request.  

Well, last week, I was trying to go back to archive a bunch of emails and I did the above search without date.  A bunch of emails popped up, but the dates went from like March 12 2014 to date and then JUne of 2013 and everything previous.  The period from Jun2013 to March 2013 was empty.  So I set up smaller search parameters.  Same to & from list as set forth above, but the dates were 2/21/2014 to 3/20/2014.  I received a return of 193 emails which promptly stopped at March 3, indicated that there were no emails between the dates from 2/21/2014 to 3/3/2014 which fell within the parameters.  That did not seem right to me.  So I did another search with the dates 2/21/2014 to 3/3/2014 with the same search terms.  I received a list of 99 responsive emails.

This is not OK.  What's up with this?  This is a short period of time and I should feel confident that I am culling all the emails within the search terms when I do such a specific search.  I do not recall this occurring say in January?  Can you please explain what the deal is?