When I was using test I had a bunch of brown amps, and they opened fine put the two white ones I had were a bitch to open. One of them broke into 50 pieces. I know how you feel. Wasting an amp sucks, especially at the end of your cycle.
I used a Dremel Rotary toll to get my Nile tops off. I had one that the top blow off. But shit I shot it anyway. My last one I just scored it with a dog nail file. I'll use anything just to get that damn top off.
I have broke them a few times and used it anyway. My reasoning was always that even if some glass was in the juice, I think the needle would be too small to drow it up. Just my $.02.