It isn't clear that A or B was marked.

I read A as being month to month from the start, and B as being a year lease that converts to month to month.

The text says "(Check A or B)" so I wonder which is checked on the document, if any. If neither is checked I still think it would have to default to 30 days.

The addendum for 45 reads as if it is intended for those with a year lease who intend to leave prior to the end of the initial year.

I also wonder when this addendum was created- whether it was part of the initial contact or added later. If added later the landlord would have needed current tenants to sign and agree in order to enforce it. Regardless, it doesn't seem to apply here.