AP Expiry Question after return visit is completed

[mib]

I have an AP approved on Jun 1st 2014 and valid for 1 year till May 31st 2015 with Multiple Entries allowed.
I went out of USA and returned back on Apr 10th 2015.
On entry immigration took one copy and on another copy as well as on passport he stamped expiry date as Apr 9th 2016. That is one year extended from the date of entry.

What does this mean.
Can I use same AP to go out of USA and return back before Apr 9th 2016?

[VisitF1]

No. You will need new AP.
I took InfoPass and visited Neward, NJ office to talk with Immi Officer and he said that I would need new AP.
At POE, they be default stamp date one year from current date. But actual expire date is the one which is printed on AP when it got approved.