If the alt isn't mentioned here, it won't count. As DBW said, if the user never posts the alt, then no harm is done because an unannounced alt cannot qualify anyway. However, if you see someone laddering on an MLT alt without it being here, you can inform the tour hosts or a mod with proof so that if they do try to post the alt after laddering later on, we can step in.
The rules clearly state participants must post their alt before laddering. Attempts to circumvent the 3 alt limit by not announcing until after finding success or the posting rule are naturally prohibited.