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Not necessairily, just because Luke and Co didn't happen to sense them means very little. This is Korriban we're talking about. The whole planet is a dark side nexus, and if the Sith simply worked to minimize their force presences, then they wouldn't be detectable in the slightest to the Jedi.
Add to that that in LOTF, Riptide and Crosscurrent the One Sith have been shown to be on Korriban and that suggests they're just very good at hiding. Also remember that Luke and Co weren't actually looking for them at the time, so it wasn't a point of focus.
It was hardly an exhaustive planetary search either. If they were on the other side of the world from a temple full of sith hiding their presence would they have sensed them? I would guess not.
When the Kesh Sith were hiding their presence for the ambush within the Jedi Temple the Jedi walked within a few feet of them and never noticed. So we DO know where thye are, but those in-universe do not.