I have found the LVC jeans waist to be more true to size versus the mainstream jeans. So i would wear a 36 in LVC versus a 34 in the mainstream 505 cut. With the mainstream 505 you need to watch the label as you will have 2 different waists - "sits below waist" - newer cut and "sits at waist" older cut we all (or most) grew up with. I am good with the "sits at waist" cut in the mainstream 505 as it is what i have been used to for 35 years. many of the large department stores have a good selection to try on for the mainstream jeans whereas the LVC 1967, 1954 etc may not be found locally.
hope this helps.