Walkalong is correct. When tools are manufactured, they are made within certain parameters, i.e.: maximum and minimum acceptable measurement. When two manufactured parts are put together, you get what is referred to as "tolerance stack", which simply means the sum of the variation between the two parts.
If your shellholder is made to maximum thickness, and your sizing die is also made to maximum length, that will give you a longer sizing length for the case when the two are set up to mate together, and the shoulder of a bottleneck case may not reach the shoulder of the sizing die.
Conversely, if each part is made to the minimum specifications, then you'll get a shorter sizing length and the shoulder of the same case can be set back too far and cause excessive case stretching when fired and lead to case head separation. All the parts are "within spec", but at opposite ends of the parameters.
Add into this equation chambers that are at the minimum SAAMI spec, or maximum spec, and you can end up with quite a distance, all within spec.
This is why it's important to set up your sizing die for the chamber the bottleneck case is going to be fired in.
Hope this helps.
Fred