I got rear axle bearings (OEM) on a hilux 1990 diesel and the same shop did rear axle bearings on a Hiace van with Koyo (japanese) on the same day. The shop owner showed me the difference after the installation. The backing plate on the Hilux axle spun freely while the backing plate on Hiace axle spun bit tight. Prior to the installation toyota bearing was bit loose but Koyo was play free.

Even Koyo is toyota's supplier, Koyo must make these bearings according to toyota's specifications. Koyo cannot make bearings on those specifications. Just like Toyota denso alternators lasts 200K miles without any service while Denso alternators on Honda's lasts 100K.