What is the current state of the federal system regarding ascertainability issues?

Federal courts have wrestled with ascertainability issues in cases where plaintiffs have sought certification of a class under rule 23 of the Federal Rules of Civil Procedure (28 U.S.C.).⁹ Although this rule does not expressly demand an ascertainable class, most courts tasked with applying it have regarded ascertainability as an implicit " threshold " requirement for certification of a class under Rule 23(b)(3). ( Sandusky Wellness Center v. MedTox Scientific (8th Cir. 2016) 821 F.3d 992, 995 ; but see Briseno v. ConAgra Foods, Inc. (9th Cir. 2017) 844 F.3d 1121, 1124-1125, fn. 4 ["we have addressed the types of alleged definitional deficiencies other courts have referred to as ascertainability issues ... through analysis of Rule 23 s enumerated requirements"].) In this context, competing views regarding ascertainability have emerged within the federal system, just as they have within the courts of this state.