I think they recovered all 13 loci but the number of matching loci is too low to qualify as a "match." One skin cell would have complete DNA, so there doesn't need to be a glob of "tissue."
I thought that maybe some of the 13 were more fragile or harder to extract than others.
Well then this beats the hell out of me.
How can they
1) extract all 13 from lax player #3 and
2) extract all 13 from the "tissue" and
3) find some that DO match but
4) find some that DON'T match
and then declare that there's any relevance at all? It seems to me that a no match on any of the 13 is a no match for the entire sample. What am I missing?