In the first place, Nissan put the Engine Plate in when they started fitting the shorter 56A transmission in cars (late 1972).

CH, if your clutch works fine, it's no problem whether you have the plate or not.

But let's say if a guy has an early 1200 and the transmission goes bad, then he buys a 56A and puts it in, then finds the clutch won't adjust correctly. Because 56A needs the matching Engine Plate, or a matching release bearing sleeve.

Good: 56L, no plate, standard bearing sleeve
Good: 56A with plate, standard bearing sleeve
BAD: 56L with plate, standard bearing sleeve

The 1200 ute came with the heavy-duty 56A from day one (1971 introduction), and didn't use a Plate. Instead it had a short bearing sleeve. After a few years they started using the Plate along with the standard bearing sleeve.

Good: 56A no plate, short bearing sleeve

When you mix and match, some combos don't work. Flywheels come in two different thickness, so that's another consideration.