] I think Mrs. Gardiner may have convinced herself that she remembered an incidence that backed up his story--but I don't know if she would have said as much outloud. I think she may have "acknowledged" it more with a smile than words?

Her character so far doesn't strike me as the type that would engage in that kind of gossip - true though it might be. She'd just met Wickham and though they had discussed Mr. Darcy (older) in positive terms, it seemed to me that her recollection of Mr. F. Darcy would have been more non-verbal.