I readily agree lack of information would not stand in the way of Mr. Collins making compliments but I fail to see how that shows he talks and thinks of rumors when he actually heard none. That Mr. Collins’ had heard of his cousin’s beauty and amiability before meeting them is in two passages in chapters 13 and 15; in one of the passages it states he would only choose one of them as a bride if they were as handsome and amiable as represented by common report—that seems like essential criteria if lack of it cancels the deal. Why should Mr. Collins pretend to himself and to Mrs. Bennet that he had heard tell of the sister’s attributes before coming to Longbourn? Why would he think he has a plan based on prior knowledge of them if he does not? He tells no one of this plan so it is not in use as part of a delicate compliment. How do you explain the passages in chapters 13 and 15 if they are not truthful of the fact Mr. Collins’ heard rumors of his cousin’s beauty and amiability prior to his visit? ;D

He had not been long seated before he complimented Mrs. Bennet on having so fine a family of daughters; said he had heard much of their beauty, but that in this instance fame had fallen short of the truth; and added, that he did not doubt her seeing them all in due time well disposed of in marriage. (Chapter 13)

Having now a good house and very sufficient income, he intended to marry; and in seeking a reconciliation with the Longbourn family he had a wife in view, as he meant to chuse one of the daughters, if he found them as handsome and amiable as they were represented by common report. This was his plan of amends -- of atonement -- for inheriting their father's estate; and he thought it an excellent one, full of eligibility and suitableness, and excessively generous and disinterested on his own part. (Chapter 15)