Extra players' credits on IMDB

Some extras have extensive credits in IMDB, like Bess Flowers, Stuart Holmes and George Bruggeman and many others. Not sure who is adding this info - or maybe there are lots of people doing it. Thanks for your input! It's nice to see that the cast lists for some movies get longer and longer every time I check.

Very strange that there are no forums on the internet where you can identify extras and bit actors from classic US movies.