Welcome Aboard, Swerve.
I am not familiar with the term Uniform Comics Code. I assume you mean the Comics Code Authority. That unabashed mess went into effect at or near the beginning of 1955. Some January issues had the seal, some didn't.
Fear of arbitrary government censorship drove almost every publisher of comics to join the CCA, or to quit publishing comics. Dell Comics, and later Gold Key Comics did not join, saying they had never published anything objectionable.
Like most forms of censorship the Comics Code (Atrocity) was arbitrary and biased. About the time Dell launched Brothers of the Spear, with a partnership of White and African adopted brothers, the Code told EC Comics that they could not show an African character doing anything important because that would offend U.S. southern readers.
The Code allowed the bad guys to smuggle drugs, but not a word could be said about why drug smuggling was bad. That suppression lasted until c1971 when The Amazing Spiderman published three issues without the CCA Seal to tell the story of drug use in general, and specifically about Harry Osborn's addiction. Those issues won awards and the Atrocity got egg on its face.
I do not know just when the CCA shut down, but not many people cared by that point.
