The rules of evidence in court generally but not totally preclude late evidence.
The only time a GJ needs to reconvene is to bring an unrelated charge. The prosecutor has discretion to modify, plea deal, etc. to lesser charges.
But as you can see, impeachment is unique in that the senate is simultaneously judge, jury, and advocates for opposing sides. They claim they are bound to follow the truth, etc., but that is a hollow promise. The outcome is as good or bad as the combined sound and moral judgment of the group. The process can certainly tolerate a good number of amoral skunks, provided they are relegated to the sidelines. What is going on here is the amoral skunks are running the public show, and the sound reasoning is ignored or summarily dismissed as “content free” or “erroneous.”
Thank you.