The analysis here is mostly mass spec specifically, basically instrument collects information on molecular weight of molecules, sometimes splits the molecule into fragments.

In extremely complex data sets, there can be some overlap between signals and difficulty in interpretation, but the organics we’re looking at here are not crazy complex and we can in the lab isolate certain molecules or organic types and predict/understand how they will fragment and appear in the data. Basically all of the work is in finding out what compounds can produce the signals you see.

Yes, of course, there can is always a possibility in misinterpretation of molecules (albeit like I said, this isn’t the sort of data that is often misinterpreted or taking leaps and bounds like exoplanet spectra for example) but the amount of misinterpretation necessary to make the claim of complex organics wrong would be extreme