Academy Ratio?

[PuppyJonathan]

I'm very confused, so I figured this place was the best to ask, I know this may not be the right subforum to talk about this but I couldn't find the one on the technical details of movies, so here may be my best bet (plus it kind of has to do with Blurays). I'm aware that mostly every movie from 1932-1950 was shot in Academy Ratio (1.37:1), but when there blurays come out the aspecet ratio of them is 1.33:1. However I did not know that the original negative is 1.33:1 but is matted down to Academy after the soundtrack is added. So is the absolute technical ratio 1.33:1, and academy ratio is just a mat? Also when the bluray comes out is it cropped to 1.33:1 or 1.37:1? I'm just very confused