First, you found it within seconds because I told you the compound name. That would not have been that simple if I had given you the raw powder pattern. Moreover, ICSD is not the first place to look in such a case. I know that you do not practice a lot identification of compounds because most powders coming at ILL are already identified. Maybe ICSD is the best database for structures of inorganic compounds, but you may need PDF-2 from ICDD in order to say what exactly is your sample to the ILL committee examining the experiment proposal.
Infallibility supposes also completeness.