its the same difference as having an aerodrome forecast that's unavailable (alternate required) and no aerodrome forecast (no alternate required unless conditions below the alternate minima).
Except the book does not distinguish between the two - in both cases you need an alternate. It does not say for a place with no forecast that you can use an alternate minima it says "must provide an alternate" furthermore it is stated twice over in the case of the location having no forecast AND an IAP.