Present what you hold. If there is enough of it in the room, the thing opens by itself.
Presenting too few shards does not produce an error. It produces a different secret, confidently and instantly, and nothing about that answer looks wrong. That is not a defect in the scheme, it is the scheme: below quorum every output is equally plausible, so the wrong ones cannot be told from the right one.
Which means this page cannot tell you whether you succeeded. Only you know what you sealed. If a threshold were enforced here it would have to know the secret to check against, and then there would be no point sealing it.