BMW TIS - not sure what it stands for in German, but its the BMW tech info system used by BMW dealers. there's a document (RA E30 11 Engine M42 1100 Engine, general - Doc name 'General instructions on dismantling and repairing engine block/crank drive (m42)') which details that its just post 9/92 cars with the check valve.
"A check valve with a rubber-lined spacing sleeve for the supply of oil to the cylinder head is installed in the engine block of M42 engines produced since 9.92"