Can mobs spawn on slabs in older versions?

[Hedghd0g]

I've been playing version 4.A9 Pustules Lancing recently and I've gotten to the point of building a brown mushroom farm, using cobblestone and wooden slabs as the floor material. However I've noticed that mobs seemingly have been able to spawn on the slabs. I know that in version 4.ABCFEFE it was changed so that mobs can spawn on any type block except wood but were there different spawning mechanics before this change was implemented? There are solid blocks beneath the slabs but I don't know if that has any effect on mobs spawning.

[dawnraider]

Prior to the spawning overhaul you mentioned, spawning rules were entirely vanilla, with the exception that mobs could not spawn on mycelium or mushroom blocks (but could spawn elsewhere in mushroom biomes), which is still true.

[Blacklands]

Just out of curiosity, why are you playing that version? Nostalgia?

[Hedghd0g]

I'm mainly playing this older version because I play a lot of alpha/beta versions of Minecraft, so the Pre-aaah early game feels much closer to the alpha/ beta early game. Nostalgia is definitely not the reason because I only discovered Better than Wolves around mid-2021, which funnily enough was through the beta version of the mod. Though I have recently started a CE world in which I was able to make my first Post-aaah windmill.