Man this conversation feels like their is just one subtle detail that neither party can seem to get across to the other. I'm sorry guys that has got to be frustrating.
So ninjas can multiclass with rogues now, then? Since it's unofficially no longer an alternate class?
*No*.
To re-quote the same RAW passage that Gisher did, but bold-face a different portion of it:
An alternate class operates exactly as a base class, save that a character who takes a level in an alternate class can never take a level in its associated class—a samurai cannot also be a cavalier, and vice versa.
I've never been under the assumption that samurai or ninjas could take cavalier or rogue archetypes.
"Unofficially" wouldn't cut it anyway (as far as, say, PFS was concerned).
Calling it an assumption without addressing any of the citations, arguments, or evidence, does not foster discussion or faith that legitimate conversation is being had.
It says right in the sentence that "a samurai cannot also be a cavalier".
Believe me: I have had my hopes and dreams of various combinations dashed on the rocks too, so much so that it's to the point that I avoid anything that even faintly smacks of trouble down the road.