The load the spring will carry is determined by the diameter of the wire and the overall straight length of the wire. Even coil springs can be thought of as a torsion spring, straightened out. If you think of one end of the straight spring wire in the vise and the other end with a vise grip plier attached, you will see that for the same diameter wire a short spring wire of say, two feet, will be quite stiff to rotate with the vise grips. On the other hand a straight spring wire of ten feet will rotate quite readily.
The Vincent springs has many coils, so it is quickly identified as a "soft spring" because it would be quite long if it were straightened out. Every little bit you cut off will make it a little bit stiffer. Generally, if a 36 lb/in spring is 16.5" or 16" is is still 36 lbs/in. The springs just have differing heights (differing spacings of the coils) and both have the same length of straight wire.
Technically, you have to "set" the spring once you get it from the manufacturer. Setting is the act of compressing the spring until coil bind occurs. It will often make the height of the springs more consistent.
Typically, the fewer coils a spring has the stiffer it will be for the same wire diameter. If you count all the coils you may need to subtract 1.5 coils to arrive at the "active" number of coils. Thus, each end of the coil spring that is flattened and ground is not counted as an active coil for 3/4 of its length (this formula may vary a bit). Any coils that are close enough to touch each other after a very small amount of movement will become inactive after they touch and bump up the stiffness of the spring.
David