We should only be concerned with those fibers that were found in incriminating locations.
Unsourced trace evidence found in incriminating locations can have innocent explanations. But, sourced trace evidence found in incriminating locations can have innocent explanations, too. So, if unsourced fibers can innocently find their way into incriminating locations than so can Ramsey fibers.
The incriminatory value of the Ramsey fibers (for the Ramseys) is low, for obvious reasons (Ramsey home). And, the unsourced fibers have some exculpatory value (for the Ramseys) because investigators went to great length to source those fibers and their efforts failed.
Investigators went so far as to tape the floors and closets of the Ramsey home. And, yet fibers (and, hairs; and DNA) that were found in incriminating locations (tape, ligatures; genital area) remain unsourced. This should not be dismissed lightly.
Unsourced trace evidence (fibers, hairs, DNA) found in incriminating locations is exactly what we could expect to find if this crime had been committed by an unknown person. Just sayin...

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AK