This part from one of the newspaper accounts is revealing:
The Rev. Dr. Fuller, of the Baptist church, accompanied the party, by invitation, as chairman, and the conversation was conducted mainly between him and Mr. Lincoln, and was not heard entire by all the members of the Convention.
And later:
Dr. Fuller expressed the opinion that the Northern States would constitute an imposing government and furnish revenue, but our informant could not follow the exact terms of the remark.
So in other words, "our informant" caught a few words here and there and pieced them together without much knowledge of the whole conversation.
Somehow over time, "And what is to become of the revenue?" got metamorphosed into "What about my tariff?" That was very convenient for Confederate and neo-Confederate propaganda.
James Buchanan left the the US in a very bad financial position in 1861. I don't know if Lincoln said what it's alleged he said, but federal revenue was clearly on everyone's mind in Washington.
It wouldn't have been hard for someone with obvious pro-secession sympathies to piece together fragments of a conversation to produce something that put Lincoln in a bad light.
Compare Lincoln's official response to the oft-reprinted newspaper story. It could well be that the "informant" mashed together Rev. Fuller's formal comments with Lincoln's informal remarks later, leaving out both Lincoln's more considered official response and much of the surrounding context, and adding a certain amount of imagination.
The Sun article is second hand (1. the source likely heard those quotes first hand, and 2. the Sun reporter wrote it down). Baldwin's testimony was first hand. He met with Lincoln and reported what Lincoln said.
The Rev. Dr. Fuller, of the Baptist church, accompanied the party, by invitation, as chairman, and the conversation was conducted mainly between him and Mr. Lincoln, and was not heard entire by all the members of the Convention.
As the article said, "... a delegation from five of the Young Men's Christian Associations of Baltimore consisting of six members of each ..." That makes at least 30 people in the delegation plus maybe Rev. Fuller. It is quite possible with a group that large that some were far enough away or maybe in the hall that they couldn't hear well. They must have heard some of it, because the article said "was not heard entire ..."
... our informant could not follow the exact terms of the remark.
I note that you have misquoted the article. The article said, "our informant could not follow the exact turn of remark." Nor "terms" and not "the." Are you trying to illustrate how things change on repeated telling by different people, a la Russian Gossip or Chinese Whispers? I concur that that no doubt happened in some of the retelling of what was said by people who weren't there.
So in other words, "our informant" caught a few words here and there and pieced them together without much knowledge of the whole conversation.
Your comment is a stretch. The informant said where he couldn't hear or perhaps the conversation went too fast for the informant to follow. But the informant appears to have heard much of the discussion, or else he would say like he did, that he couldn't follow this part or that part.
Somehow over time, "And what is to become of the revenue?" got metamorphosed into "What about my tariff?"
The tariff quote might have its origin in Baldwin's Memoir as reported by Robert L Dabney in 1876 (based on an 1865 interview with Baldwin) and also reported his book, "Discussions with Robert L. Dabney, Volume 4." Here is an excerpt of the 1876 article and a confirmation of its substantial correctness by someone Baldwin told when he returned from Washington in April 1861. Lincoln's words below are shown in bold red font. [Source: see Link].
Lincoln seemed impressed by his solemnity, and asked a few questions: "But what am I to do meantime with those men at Montgomery? Am I to let them go on?" "Yes, sir," replied Colonel Baldwin, decisively, "until they can be peaceably brought back." "And open Charleston, &c., as ports of entry, with their ten per cent. tariff. What, then, would become of my tariff?" This last question he announced with such emphasis, as showed that in his view it decided the whole matter. He then indicated that the interview was at an end, and dismissed Colonel Baldwin, without promising anything more definite.
In order to confirm the accuracy of my own memory, I have submitted the above narrative to the Honorable A. H. H. Stuart, Colonel Baldwin's neighbor and political associate, and the only surviving member of the commission soon after sent from the Virginia Convention to Washington. In a letter to me, he says: "When Colonel Baldwin returned to Richmond, he reported to the four gentlemen above named, and to Mr. Samuel Price, of Greenbrier, the substance of his interview with Lincoln substantially as he stated it to you."
Similar, as I've pointed out before, to the way today's dishonest media takes Donald Trump's words out of context to make him sound silly, or heartless.
It's an age-old practice which works especially well when people don't know all the facts, and wish to believe the worst.