I know that with plants there can be an Inbred Depression that will not show itself until 100's if not 1000's of generations of clone from the seed, I know this because my 91 year old Uncle was a breeder of potatoes and corn and wheat and soybeans, well you name it he bred it from around 1946 to present day. I do believe that if you were to clone a clone, and so on for 25 years you would have degradation of the basic cellular structure required to do its job properly and it would lose its vigor and potency and yield characteristics.
I think people like to assume based on facts they saw in the latest sci-fi thriller about cloning, that it is infallible, which is not the case, a plant loses something on a cellular level every single time its cloned, I do not base this on any sort of science except for what I have witnessed or been a part of first hand, and that is plants do not clone themselves in nature, the species either inbreeds if possible or if left alone in the wild chances are it will pop its own seeds as a type of defense mechanism to ensure the species is continued, if you ever have the patience and yield to experiment, try letting any strain completely mature and die on the stalk...chances are you will find seeds on the outermost edges if your strain has any hint of landrace or ruderalis genetics in it.