Several of the witnesses in the later court scene are said to be "under oath," but none have actually been sworn in by the court clerk.
The second time that Virginia Colfax (a.k.a. Helen Bynum) is on the witness stand, she can also be seen in the spectator area (when the camera cuts back to a shot of the defendant). This happens as she is being questioned by Perry Mason after she tells him that it was Frank Livesy who told her to pose as Della Street.
Denby and Livesey postpone a stockholders meeting when they learn that Edward Garvin has been arrested for the murder of his former wife Ethel. They (and Perry Mason and Edward Garvin, as well) should have done that days earlier, upon learning that Ethel was taking signatures for fraudulent proxies.
Perry learns through Paul that a hotel in Mexico turns off its clock chimes after ten at night. Perry is a previous guest at that hotel and would already know that.