Hideki Imaizumi, producer of Crisis Core, talked about the "Last Order" anime OVA (pictured) with IGN. Released as a bonus with Advent Children in Japan, the animated short also focused on Zack and the role he played in Nibelheim. "When we made that feature, we changed the presentation of that event from the original Final Fantasy VII. And the fan response was - well, there was considerable negative feedback in regard to changing a part of the story that they considered integral to the whole lore."
Thankfully, Crisis Core was able to set things straight, restoring the canon that so many Final Fantasy VII devotees pore over. "So we listened to that and learned from that. And in fact the Nibelheim incident is presented again in Crisis Core, and we were careful not to make the same decisions that we did in Last Order."