] Mr. Gardiner was just evading a direct recital of how Wickham, and Lydia were discovered. He never mentions Darcy's part in his subsequent letters to Mr. Bennet, even when he was asked about the money he had put forth to 'save' Lydia.

I suspect Mr. Gardiner might have been aware of his brother-in-law's indolence, and counted on inquiry to the particulars ever being made. Now that Lydia's reputation has been more or less salvaged, Mr. Bennet will probably go back to giving her as little thought as possible.