Lol, no you can't. You'll get hit.
In every situation? That's ridiculous. Again, I'm not talking about chicken blocking. You seem to think that there are no situations where jumping back and blocking doesn't get you out of trouble or is not a really good choice (P4A).
I'm bringing up other games because if people are reacting to things that are faster than 19 frames, how are you going to say a 19 frame overhead is unreactable?
All frame data is not created equal. In SF4 on PS3 and Xbox360, there are 2 frames of difference in the game's input delays. Essentially, this means you have 2 less frames to react on PS3 as opposed to 360. Now that is one game (the same exact game), in which some mixups are unreactable on one console, but reactable on the other.
I've heard that TTT2 has like 7-9 frames of input delay built into the game, whereas other games only have 2-3. IMO, Injustice is one of the most unresponsive games out there. There could be anywhere from 7-12 frames of input delay, but nobody (to my knowledge) has calculated this. Then there is the possibility of frames between standing and ducking, which could add 1-3 more frames to the delay (again, I have no idea). After all is said and done, you may actually only have 10 or so frames to react to the slide/F3.