At least in the case of T2, digital VFX were hard-matted at 2.00:1 as a compromise between saving render time and giving room to reframe later. "The Abyss" would be an interesting one to find out because only one sequence contains digital effects (two in the SE) and all but one shot of the Pseudopod sequence was composited optically.

The screener VCD copy of "The Matrix" contains more of the Super 35 area than was clearly intended to be seen (some examples pointed out on its thread) and at least one CG effect of a bullet flying towards the screen was hard-matted all the way but composited over the full-frame. The Wachowskis refused to release a Fullscreen DVD and I recall looking at an examples page years ago that showed the VHS version as completely cropped during numerous scenes.