Re: Episode of the Week : The Enemy Within
What happened to Kirk's insignia when he was wearing his gold shirt? Cushman (2013) says that the badges were removed each night when the uniforms were sent off for cleaning. When somebody forgot to sew it back on the next day, in their frantic race to meet airdates and shoot quickly, everyone assumed it was an intentional omission ordered by someone or other, and nobody questioned it.
"Sometimes I get the feeling the only way we could achieve a STAR TREK segment on budget would be to have 60 minutes of Mr. Spock playing kazoo solo as Captain Kirk holds him in his arms while standing in a telephone booth."
Bob Justman, 1967.