In the old days, such concerns over that kind of trivia didn't matter. But then they had no idea in those days that their shows would live on in syndication, then VHS, DVD, and now digital storage to be viewed over and over and over again by fans.
The apartment number for the Ricardos on 'I Love Lucy' changed all the time if it got mentioned in the script. For example, in "Ricky And Fred Are TV Fans", the apartment number was 3-B. But one time it was deliberately changed to fit the needs of the script: in an episode in which Lucy made a bet that she could go a whole day without lying, she said in an audition that she had been in 3-D, when asked if she had any experience.
To rectify that Zonk? Maybe the Mertzes converted one of the apartments on the third floor into two separate studio apartments, or combined two apartments into a larger suite. Either way, it would have led to the numbering system for that floor to be re-designated.BCnU!