The number of windows in Morrolan's tower seems to vary from moment to moment, and depending on who is doing the counting.
Morrolan's Window presumably uses Necromantic Gates to open passageways between different planes of existence. Since the tower was originally built as a place for Morrolan to commune with Verra privately, it's appropriate that the window(s) are hinted to give passage into Verra's Halls as well.
The existence of this window is considered an Imperial secret, known only to a select few individuals. Considering the possibility of using these necromantic gates in reverse, it would be unwise to allow the Jenoine to learn of the window(s).