The network let the creators go back to the drawing board, and they ultimately decided to keep what worked, which was Sheldon and Leonard, and they reworked almost everything else.
In a way, Kunal Nayyar’s story and the evolution of Raj is similar to what happened with the overall show.
As part of that rework, they auditioned actors for several new characters including Penny, Howard and the aforementioned Dave.
The original pilot was shot and did not go particularly well.