> Do you mean that the titlebar would be off screen so you couldn't move/close the window?

Not just the title bar, but often also e.g. half of the settings and the Cancel/Save/Ok buttons.

Basically the screen was 600 pixels in height, but the modal was designed after 2005 so it was 768 pixels tall, and you would get a cropped modal missing maybe 10% top and 10% bottom pixels that you couldn't interact with via mouse, and you couldn't resize nor move (either because it was fixed size, or because all corners that would allow you to do so were off-screen).