Having not read through all 6 pages of the linked post, I will ad this to the mix.
You can actually pass along a thermophilic mother culture with desirable bacteria without the need of further inoculation by starter cultures. This can be done by heat treating the culture mix in order to kill off everything, and then incubating at certain temperatures. With some understanding of how this all works, we can maintain a strong culture for generations -an entire year or even more if we freeze it periodically and re incubate.
But this requires the use of raw milk. With pasteurized milk you pretty much have to restart all the time. With raw milk, we actually lose the original cultures and replace them with wild strains. This is how we avoid the issues of mutation and so forth.
This is essentially what we do to produce our whey starters, we heat treat a portion of whey to isolate streptococcus thermophilus (not really isolate as much as make it the dominant strain) and then mix in another culture treated to isolate lactobacilli. Our ratios are not exact, but they also do not have to be. The time factors involved in lb production and the long aging terms mean that the exact populations are not critical for us.
But this is all complicated stuff, and don't do it if you don't know what you are doing. The processes we used were figured out bu generations of trial and error. It's not something you are going to just figure out in your kitchen one evening.