They did that to my buddy's last 2 cans( he just got them a month ago). 1 was approved 3 months before his 2nd and they waited to ship both stamps until the 2nd was approved. But I have also heard of other guys getting them seperate. Who knows.....
I recently had two cans on the same form 4. both were approved on same day and stamps delivered to SOT on the same day. while that would "make sense" it seems frequent to have a scenario like you describe where multiple cans on same form 4 take different times. yay govt.