What is the test for impeaching a judgment or verdict based upon evidence that merely discloses unusual circumstances?

" 'Although an appellate court will not uphold a judgment or verdict based upon evidence inherently improbable, testimony which merely discloses unusual circumstances does not come within that category. [Citation.] To warrant the rejection of the statements given by a witness who has been believed by a trial court, there must exist either a physical impossibility that they are true, or their falsity must be apparent without resorting to inferences or deductions. [Citations.] Conflicts and even testimony which is subject to justifiable suspicion do not justify the reversal of a judgment, for it is the exclusive province of the trial judge or jury to determine the credibility of a witness and the truth or falsity of the facts upon which a determination depends.' " (People v. Thornton (1974) 11 Cal.3d 738, 754.) Here, Witnesses Nos. 14, 15, and 16 properly were impeached by the factors defendant cites (except for counsel's discovery after trial of Witness No. 15's sentence (see post, pt. II.C.6.)), but nothing about their testimony was inherently unbelievable or implausible.