Great question — answering as the UphillTech team:
IMDb credits are generated by the filmmakers themselves (for smaller, independent productions) or representatives for the filmmakers/producers. On occasion crew and cast members get left off the submission form. I speak from experience as I appear as three different entities on IMDb because the filmmakers I worked for neglected to see if I was already represented and created a new page for me each time. This is certainly the case with other actors/crew members, and could go some way to explaining the discrepancies you have discovered. Bottom line is IMDb is not infallible, and it would indeed require some serious cross-checking with other sites in order to confirm the actor you are...
Full answer by Nobby: https://movies.stackexchange.com/a/1726 (CC BY-SA 3.0).
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