iPhoto Events & Photo Stream

Recently imported 400+ photos from iPhone to new MPB iPhoto. In the PHOTOS section, most of the imports are organized by event (the date photos were taken), but there are several cases where there are no dated events but rather a header like, "April 2013 Photo Stream April 1-30, 2013" containing all my April photos. What confuses me is that there are no separate, dated events in April.

Also wondering if, as photos fall off my Photo Stream, if they will also be deleted from the photo stream headers in iPhoto mentioned above.

Thanks for any help.
Steve H

Im not to sure why this would be happening if all pictures are from the same gereal date, but in iphoto preffernces there is a tab that deals with how the events get catagorized, just make sure the settings are all correct to what you want.

And for your other question, No they do not delete. There in theevents tab

Thanks for your help.