Yes, I was aware of that. The opening credits were filmed just after the assassination and in Long Beach, CA, I believe. You have to look carefully as the flag only appears for about a second.
Nowadays it seems that the flag is always at half-mast because somebody stubbed their toe, or something.
Long Beach? It always appeared to be Marina Del Rey. I will have to watch again. I never knew that, that the flag was half mast for President Kennedy. Wow.