How can I know if my lithographs are originals from the date of the 50s or copies of copies??

Make appointment with the museum

Call the museum and ask them how to athentic them

I wish you had been a little more specific...are these lithographs in your possession now or will you be purchasing them in the near future? If you have them in your possession now, I'm sure you can get in touch with the museum's staff and they will have answers to your questions? They are very helpful and knowledgeable.

Good question. But I don't know.