You need to check each COL you read to find out what it means. It may mean the COL listed is simply the one used for the testing the manual writers did to get the data. It may be the SAAMI listed maximum length. It may be a dimension a reloader is using in his specific rifle. It is unlikely to be a "minimum" of any sort.
Reloaders do vary COL quite a bit, but only after careful consideration of factors like the maximum length of the chamber in the specific rifle, amount of bullet "jump" to reach the lands, length of bullet being held by the case neck, intrusion of the bullet into the case powder space, magazine length, and other factors.
Before you use a listed COL as a basis for your decisions, make sure you understand what it means in the specific case you are reading about, and in your own specific rifle.