- There is a single monster that can freely transport between the pocket universe and our world. But then why wouldn't it simply attack people in the house?
I prefer this one, the monster in 1974 is kind of like a "ghost" in that one can only catch glimpses of it, and that certain conditions must be met for it to catch somebody.
Hell, we don't exactly know how Tacorian got trapped there, for all we know it feeds off time (Artron?) energy or something and that's how it creates the pocket 'verse and sustains it.
They can give ANYTHING a timey-wimey explanation!