When did it become against nec code to put a electrical panel in a bathroom

You will need to contact the National Fire Protection Association to see if someone there can do the research and find the answer to your question.

The National Electric Code changes every three years. I have been dealing with it for 38 years, and lived through 13 editions. The challenge is to learn and understand each new edition, and don't look back.

The oldest NEC book I have is 1999 and it is prohibited then.