proper form has more to do with certain leverage positions while actually performing the lift....take squat for example...people can change stance width, grip width, head position, elbow position, bar position, etc...but during the lift, the body typically has only one way to complete the lift in a safe and effective manner...hips should never rise before knees coming out of the hole, your upper torso position should never be compromised, your spine should stay in as close to a neutral position as possible, your knees should never cave excessively, etc etc...
same as with deadlift...hips should only move forward and "through" the bar, never hinge backwards and cause your upper body to become parallel with the floor, neutral spine, very little rounding specifically in your lower back, no Halloween Cat impersonations...but grip width, stance width, hip height, etc all can be individualized....but you can freeze frame almost all top lifters and see almost identical positioning while the lift is actually being completed...