What is the test for a motion to amend the statute of limitations for an amended complaint?

This court granted extraordinary relief, holding defendant's demurrer to the second amended complaint should have been sustained with leave to amend "for the sole purpose of allowing plaintiffs to specifically plead why the statute [of] limitations is inapplicable." (Gavasieh v. Superior Court (Jan. 29, 2016, B266980) [nonpub. opn.] (see fn.1).) We added, the "proof of service creates a rebuttable presumption that a document was in fact mailed. (Evid. Code, 641.) However, if the claim rejection forms were never received at the address listed on the proof of service, this creates a triable controversy as to whether they were mailed in the first place. . . . Obviously, [however,] if plaintiffs fail to more specifically allege the facts underlying their nonreceipt of the claim rejection forms, respondent court will be well justified in dismissing the operative pleading." (Ibid.)