Any time you have a flavor that has a vanilla-custardy type note to it, it will have one or both of acetyl propionyl and acetoin. There is also the possibility that there will be Diacetyl as an added ingredient, (the flavor manufacturing company that we purchase our flavors from is restricted by their insurance from using Diacetyl as an ingredient, because of employee environmental health issues, but this is not true of all flavor manufacturing companies).
Our vanilla custard is a good example. Pretty much by definition, a vanilla custard flavor, no matter who makes it, will have both acetoin and acetyl propionyl (or diacetyl) in it. Just like it would be hard to bake a cinnamon cookie with no cinnamon, it would be really hard (pretty much impossible) to create a vanilla custard flavor with no acetoin or acetyl propionyl (or diacetyl).