In the case of Kubrick, it gets complicated. IIRC, there is a storyboard glimpsed on the Blu Ray supplements for The Shining that clearly shows the intended theatrical ratio. Might be some framing marks on a playback monitor as well.

Stanley personally supervised the Dr. Strangelove transfer for the Criterion LD, and that had alternating full frame and 1:66 ratios. Had widescreen tv's been more common before his death, (and the DVD format taken off) it's likely he would have approved more theatrical ratios for his other films.

Save for an early 80's pressing, 2001 was properly letterboxed in all the LD incarnations I own. It even aired on TNT in widescreen several times in the 90's.

There was a lot of teeth gnashing over the Barry Lyndon Blu Ray over at the HTF. It's a slightly different aspect ratio from previous widescreen releases.

I ran The Matrix DVD in sync with a TBS showing once before digital tv came along, and the framing differences were interesting.