I have always believed there is no problem with cloning a clone and making a new mother. However, after reading this I might start trying to keep my seed plant as the mother with bonsai technique. "Why plant 'clones' aren't identical" http://www.ox.ac.uk/media/news_stories/2011/110729.html
With foresight and excellent pruning skills, og moms(seed mothers) can provide clones for decades. I know of landrace genetics still alive after 30 years. Some of the drawbacks to this, is that once plants reach a certain age, certain hormone levels drop. The interpretation of certain "triggers" are not as quick or pronounced. Such as the ability to change it's metabolism and produce roots from stem sets(cloning), or it's phototropic response to short daylight hours, making cloning and flowering more difficult. I have cuts that were from cut's etc... but, I believe the best possible scenario would be to replace mothers every 2-3 years with mothers from fresh, viable seed stock, although I know this is not always possible. I liked the article! Peace!