To my great surprise, an open pack of Ilford Multigrade II RC (yes, II) I've had for two years, and that I finally tested a couple days ago, was perfectly usable. No fogging at all. Never judge your MG by its number...

During the same test session, Kodak Bromide, unknown origin and storage, and expired in 1970, showed slight fogging but should be usable with benzotriazole added to the developer.

ORWO papers from the same era seem to be more likely fine than fogged.