I have just confirmed there is a major inconsistency error with the letter sent to Hoffmann that says "I know who you are" and we first saw in SAW 5.

At the end of SAW 7, a flashback shows that Dr. Gordon is the one that sent the letter to Hoffmann . However, in SAW 5 its implied that it was sent by Jigsaw himself because Hoffmann receives it right after he kills Seth so he hadnt become Jigsaw's helper yet, thus Dr. Gordon had NOT have even been tested yet.

In fact, the flashback scene in SAW 7 is not the same as the original scene in SAW 5. It was re-shot since Hoffmann is even wearing a different suit and tie. What happened there?