Go in practice mode. Set opponent to block at the first opening he gets. Try doing anything after forward + square. It's blockable because the stab takes too long to recover. So once again, no, it's not possible.
if you set the cou to block obviously but against a moving target or if you do it from behind how will the person react in time to guard or roll? Especially, online. Don't think those players will intentionally guard you and only you when there are other worries like 2 other opponents.
Not sure if serious.
You truly need to fight some actual decent players. Something that is not a combo doesn't suddenly become a combo just because the occasional online scrub fall for it.
Whether an opponent is facing backwards or moving, there is no follow-up potential from Sir Dan's stab. There's no inhuman reactions or anticipating required. I get hit by the stab, I get a huge window where Sir Dan is recovering. I just hold block or evade roll. Even an amateur could escape it once they know about it. The move only being useful alongside a partner is exactly why it's a terrible move. I shouldn't have edited my original post because forward+square is infinitely worse than down+square.