I’m not sure either way will work. The add() method creates the event, so b1[i] doesn’t exist until after you call b1[i].add(), which creates the element b1[i].a. Then you can call b1[i].a.wait_ptrigger(), but the add() method also triggers the event before you call wait_ptrigger(). Since it’s apparently in the same time-slice, wait_ptrigger() will return immediately.
Not sure what you mean by “resume an event.”