I've checked the Mega Drive original and this one, both PAL versions due to the password function. The former was easier to get to the level due to button based level skip cheat.

It's designed like this as Scud is made up of sprites on both versions, no extra tiles beyond what you can see. Probably due to keeping it under the sprite limit since there's also the HUD, Woody/Roller Bob, stars, rockets and cans. All of those are sprites too in both versions. The MD version has very little breathing space in the VDP for anything else while the SNES version has a bit of the level intro loaded as well. Also checked the ROM in the SNES version, it's again what you can see in game.

Also since the SNES cheats that are online don't work for the PAL version, ended up making a couple. 7E0006:01 for the level skip then press Start in game and then Select, 7E0021:04 for infinite health and 7E0023:03 for infinite lives. Ended up having to use these to get to this level.

Makes me wonder if it has additional tiles in the VRAM or even being visible within the vSNES scene viewer.