Another important, yet often overlooked aspect when evaluating spectral library searching results is the confidence that is ascribed to the original library annotation. If an original library spectrum is incorrectly annotated, this error will propagate through all future studies that find a match to this library spectrum. Consequently, even when a match is obtained, the researcher should still make sure that this makes sense in the context of their experiment. Therefore, it is paramount that library spectra are of the highest possible quality and that their provenance is tracked, so that the end user can understand the origin of their spectral library annotations. Having a clear understanding of the provenance of reference MS/MS spectra is especially relevant when spectral libraries are crowd-sourced, with spectral data coming from heterogeneous sources with potentially differing quality levels, although mistakes have also been found in commercial spectral libraries.