rs. That task can be decidedly difficult, especially given that Plaintiffs premise their [' 934] class in part on a disparate treatment theory. See Stastny v. S. Bell Tel. & Tel. Co., 628 F.2d 267, 274 n.10 (4th Cir. 1980); see also Garcia v. Johanns, 444 F.3d 625, 633, 370 U.S. App. D.C. 280 (D.C. Cir