To be admissible, prior events or accidents must be substantially similar to those at issue in trial.

United States v. Schuler, 458 F.3d 1148, 1154-1155 (10th Cir. 2006) (convictions for mail fraud and money laundering; defendant contended that her cross-examination on previous instances of credit card fraud and identity theft was improper under Federal Rule of Evidence 404(b); convictions affirmed; court...If a crime or act by a witness did not result in a criminal conviction but is probative of truthfulness and not unduly prejudicial, it may sometimes be used to impeach the witness.

Fed. R. Evid. 602 advisory committee's note ("It will be observed that the rule [requiring personal knowledge] is in fact a specialized application of the provisions of Rule 104(b) on conditional relevancy.").A person has the personal knowledge that a witness must have if and only if the evidence is sufficient to permit a reasonable trier of fact to conclude that the witness personally perceived the matter. The preliminary question of personal knowledge is governed by the standard of whether the evidence is sufficient to allow a reasonable person to conclude that the person has personal knowledge; the applicable standard is not the more demanding preponderance of the evidence standard.

Santa Barbara Capital Mgmt. v. Neilson (In re Slatkin), 525 F.3d 805, 812-813 (9th Cir. 2008) (holding, in plaintiff trustee's adversary proceeding against defendant investors, that the bankruptcy court properly admitted the debtor's plea agreement....A statement is admissible under the hearsay exception created by Federal Rule of Evidence 807 or a comparable State rule only if circumstantial evidence shows that the affected statement is as trustworthy as the statements that are made admissible by the hearsay exceptions created by Federal Rules of Evidence 803 and 804 or by comparable State rules.