Some samples may reflect stereotypes and prejudice of their times and original creators. They may express racial prejudice, sexism, social stereotypes, ignorance and/or poor knowledge of other cultures (for instance accents that are deemed insulting today).
The views and opinions expressed in these are those of their original creators and do not necessarily reflect my opinions.
I verify that the source videos are in the Public Domain by searching the web, there are lists of PD movies and websites dedicated to them. Before I decide to use a video, I find at least 2 sources that say it is Public Domain. Of course I try to avoid errors but I am not giving any legal guarantees about the PD status of any source video either.
Also, here in North America, there are bargain-price DVD labels that offer PD movies. Many of the movies I have used come from my personal collection of such DVDs.