I can't be alone in having this happen with expired polaroid sheets. You load the holder and pull and pull on the tab but the envelope will not pull out. Somehow through moisture or whatever a part of the negative has become stuck to the sides of the envelope. Even with the tab clipped at the bottom, your attempts to slide the envelope out remains fruitless regardless the force exerted.
This guy regularly takes such sheets into the darkroom. He removes the tab, loosens the sheet from the envelope, puts everything back together and saves the day.
Here's a video clip of how he does it...
Resurrect your stuck 4x5 Polaroid
