I was not saying I did not believe the exposure could have occurred as written rather I was thinking about why it did happen the way it was written. (:D)

I agree Darcy may not have thought Col Fitzwilliam would figure out who he saved but that is not much guarantee he will not repeat the story and when Darcy finds Lizzy at Hunsford I think he would want to assure that story does not pop out of his cousin in front of her. I feel it was incautious not to warn Col Fitzwilliam Lizzy knows the lady of his story. It does not really matter if the colonel had figured out it was Bingley or not just that warning could have prevented exposure. It is a mistake on Darcy’s part. Of course it is a mistake that pushes the story along.

My point was perhaps it was not so sensitive of Col Fitzwilliam to joke about Darcy’s separating Bingley from a lady he liked because of those “strong objections” as he might have realized Lizzy could find herself in the same position—a lady with little more to offer than her affection and personal charms. I guess this did not cross the colonel’s mind and it could be he does not know Lizzy’s situation or he was carried away by enthusiasm as you suggested.

I think it is likely Col Fitzwilliam knows something of Lizzy’s marriageability. Mr. Collins is a blabber-mouth. Lady Catherine does know of the entail (29) and has probably been told how much Lizzy’s parents could give her on marriage and what her connections are at the very least—basically what Lizzy has to offer in a marriage besides her lovely self. What he did not offer up on his own Lady Catherine would have no scruples asking for. In Ch. 8 the Netherfield party discusses Jane & Lizzy’s low chances of making a good marriage as soon as Lizzy leaves the room. I can see this type of discussion going on at Rosings about Mrs. Collins’ friend led in a most authoritative manner by Lady Catherine and I can also see it happening between Darcy and Col Fitzwilliam.