(1) Is this a California case (because you refer to "KC §§ 1709 , 1710")? (2) Do you want to add 12 OR 27 new causes of action? And, (3) regardless of (1) and (2), under the relation back doctrine, if the new cause(s) of action is/are based on the same general set of facts as those in the original complaint, the amended complaint will relate back to the date of filing of the original complaint.
Whether a claim is timely because of the operation of a relation back depends on the actions alleged to support that result. You've said nothing about the facts on which the alleged relation back would be considered valid or not. No meaningful comment can be offered in the absence of the facts that control the result here.
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In California, you generally have the right to amend your complaint at any time, subject to filing a motion and getting leave from the court.
If your new causes of action are based on the same claims as your original causes of action, then you should be allowed to amend.
Your claims appear to be complicated. You should consult with a local attorney.
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