There's no info on filming dates, but ...
... if the cameras were rolling any time toward the end of January, then there were four birthdays among the principals to celebrate. Jean Simmons, Suzanne Pleshette, Katharine Ross and Delbert Mann were all born within 2 days of each other. Just an odd thing I noticed when surfing bios.
You know me. I'm the same as you. It's two in the morning and I don't know nobody.