Well then to say there is no new knowledge to be gained in History is simply untrue, by the standards we agree to.
There is a good deal of information on an unmarked flash drive, in a box, in a secured vault, in a department of defense site, in rural Pennsylvania. You can only access it by requesting it specifically, and if you don't know what it is, good luck with that.
I am the only person in the entire world who knows the contents of that flash drive. It is a transcription and audio file of a conversation between two humans who are dead.
It's got some rather important information on it, and this is the level of work that an unpaid intern does while working on a history degree.
That's just the research end of things.
If we consider integrated knowledge to be knowledge, for example if we consider Newton's theories to be new knowledge even though the motion of objects was already
observed, then Historians produce new knowledge even more regularly.
If I integrate individual known facts about 16th century Ireland, and come up with a new causal model for why and how the Nine Years War was started, something that wasn't even understood when it happened, I've also contributed new knowledge.