Six Degrees also started out downstairs and moved up. Stockard had a tv commitment or something and left the cast for a few months after the transfer and Swoosie Kurtz took over for that period. (I had a semi-heated discussion with the box office when I wanted to exchange the ticket I had bought based on Stockard's reviews after her temporary leave was announced, and they tried to give me the line about her not being above the title, and I wouldn't budge. I won.) Kelly Bishop was Stockard's standby and played the role, too.
But Blue Leaves started downstairs, moved up to the Beaumont just in time for the Tony cut-off and then moved to the Plymouth in the fall. I saw it in all three venues with Stockard, her understudy (since I was comped during previews) and Baranski in the same role.
At the time the theatre world all knew Stockard was practically at death's door and was missing all the previews, but Lincoln Center couldn't delay the opening because they were like 2-3 days from the cut-off. Stockard being the trouper she is, rose from her sick bed and did the performance.
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher