Especially considering even Inmarsat has acknowledged also the possibility of that data being spoofed (although they think it's very unlikely):
In terms of evidence the data suffers from the same contamination issues as any crime scene investigation: chain of custody (CoC). Who handled it? Could anyone have misplaced or mangled it, even just by accident? Is there a clear trace from receiver to storage with checksums and fingerprinting of every action? Probably not as the pings were not used for this kind of investigation before. Only for that reason it should be treated as a promising but still single line of evidence no matter how sound the mathematics would be. It's only as good as its source, after all, a source which without proper precautions and protocols in place is simply not a closed case (but all they got here).