Redemption was always a massive threat to the rule of two, but flying under the radar like the rule called for pretty well negated the chance that the jedi would notice and expend significant effort attempting it. Darth bane acknowledged that the jedi unity was their biggest strength, and lack of unity was the sith's greatest weakness.
He recognized the only way for the sith to survive was the rule of two, in order to slide under the radar of the jedi. Become invisible, basically.