Swiss and burgundian emergences

[NodachiSam]

I've never in all my playing ever seen the swiss or burgundians show up so I wonder if it is even possible. From the game files they look like they could function perfectly like normal factions and I hear they are in multiplayer but are they ever in single player? Presumably they are able to appear like the Mongols are able to appear even though they do not exist at the beginning of early and high.