You guys should test this too, but what I find is that there are 2 different sets of plus/minus on block for all d1 and d3s.
There is a normal plus/minus amount, and then there's a plus/minus amount for when you release block on the first possible frame.
I find that in the first case it is always consistent, and in the second case it always causes zero blockstun.
That's why some frame data has certain moves (like kitana d1) at - a huge amount, when in gameplay it obviously isn't that minus most of the time, or it would be punished way more.
And with that in mind, as far as I know, Jax's d3 is plus on block normally, without the blockstun bug.