Not sure I can put this into words properly but after reading through the Stone indictment, it is clear, to me, that if it were not for his testimony, he didn't actually DO anything wrong at all.

They are only charging him with things he said or did not say to THEM as a result of these investigations.

Meaning that if he hadn't testified, there was nothing to charge him with.

The ONLY wrongdoings being charged were as a result of or triggered by him agreeing to testified.