It was not originally scripted for Blanche to have a Southern accent. Instead, it was Rue McClanahan's idea to introduce it.
The actresses consumed over 100 cheesecakes during the show's seven-year run. Bakeries from around the USA would send in cheesecakes for them. Bea Arthur hated cheesecake in real life.
When the show first aired, Queen Elizabeth the Queen Mother loved it so much that she wrote to the four actresses and asked them to perform a live show especially for her. They obliged, and acted out a sketch during the The Royal Variety Performance 1988 (1988), at which the Queen Mother was present, in which the girls are depicted onstage visiting London, first interacting with the host Ronnie Corbett and then sitting down for dinner, recreating various moments from previous episodes.
Rue McClanahan had a clause written into her contract that she be allowed to keep all of Blanche's custom-made clothing. McClanahan had 13 closets filled with the designer wardrobe in her Sutton Place co-op in Manhattan.
During the "Herring War" story that Rose tells, Rue and Bea break character and the scene got so out of hand that they were going to cut it from the episode entirely, but they kept it in the episode to show just how good the comedy in the show could be.