cameo (such as COCOX in LYARD) or a non-creidited role (such as RSCHN in a few ASAND films or ALAPA in ANLY2) . Of course the press kit may also be misleading, but I will not mention the millisecond onscreen role that got credited almost a decade ago.
If you have information by having seen a screening, feel free to post it as Antibody/DMac does consider that information. Sooner or later, it all works out.