Cotton Alley levels are Bonus1-1 for level 7-1, and Bonus1-1x for 7-1x.
Retro are (world)-(Level). For Meat is dead 3, It would be 5-12.
Easiest way to find the level name is to make a replay of it.
Umm... What do you mean 5-12 is Retro? It loads a regular level for me...