So this is what i found on other thread about background check
Not needed at this time" means that your BG check went to the next stage. "Not started" means your application has not been accessed by officer yet. "In progress" means your application is started and CIO is checking the provided docs. At this time your meds are passed, criminality/RCMP screening and biographic (if applicable) are in progress. When it changes to "not needed" it means your criminality is completed, RCMP and biographic is completed, security check and eligibility is in progress and coming soon. When your last BG check stage is going to be completed (security passed) it will go back to "in progress" (though it might never gonna change since now) and your secondary visa office will start the final decision based on eligibility. After short period of time you will get your result
http://www.canadavisa.com/canada-immigration-discussion-board/my-background-check-wentt-from-in-progress-to-not-needed-at-this-time-t385125.345.html
hope u guys find some help with this.Also there was some may applicants different dates who got ppr in April before anyone of may got it.