Given the way the FSS were greased in at least one other case how much credibility can be placed on anything they said in the McCann case ? By their own admissions there are "grey areas". So they said "nah 't ain't anything to do with MM, conclusively"; much the same way as they said "oh yes 'twas Sean Hoey conclusively". Well we now the latter was bollocks as upheld by an English court and basically upheld by evidence given by the originator of the LCN technique. How much do you want to lay on the former being true?
Then there is the issue of their[FSS] representatives refusing to be interviewed by Summers and Swann.
What's odd about that? Actually, a mystified spokesman did speak to the media (and was recorded on audio)... basicly saying that the FSS hadn't a clue how the media had come to the conclusions that were appearing in the media as the tests hadn't yet been concluded.
I may still have a link somewhere, but no guarantees, I'm afraid.
Beyond that, I'm not surprised that the FSS didn't want to be interviewed. They'd be in the same awkward position as LP if they were quoted on the garbled understanding that the original PJ team came to.
ETA: It's true that they couldn't say one way or another whether the compatible components were hers or the result of a combination of the other donors's ones.
But even if it HAD been her DNA in the car... there are perfectly legitimate explanations as to how that DNA could have been found in it. So there's no reason to lie or attempt to cover it up.