Milk fell into a pot of meat. Before you realized that the milk fell in, you added water to the pot. Then you found out that milk fell into the pot before you added water. Without the added water you don’t have enough רוטב in the pot to be מבטל the milk, with the added water you have just enough to be מבטל the milk. Is the food/pot kosher or trief?
Shulchan orech yore dea siman 99 in the Shach paskens that chaticho naases neveila (the whole mixture becoming treif that consists of the according to the rema - more than a 60th of any isur E.g pig,and mechaber holds only when milk is mixed with meat would this halacha apply) even with no knowledge of the mixture at first but then subsequently knowing about the mixture after more heter has been added.
So you would need 60 times the amount of issur and heter together,in a pot that had less than 60 times heter than isur. e.g you added 20 pieces of kosher meat to 1 piece treif meat in a wet mixture you would now need 20 x 60 equals 1200 times the piece of treif assuming this was all done by mistake.
Even though the Darkei Moshe brings down the opinion of the Issur vaheter ho-oruch that lack of knowledge suspends the mixture from becoming a neveila (and adding more heter even with a gap will nullify the orriginal Issur once the heater is 60 times more), Rabbi Akiva Eiger (quoted Pischei Teshuva 99,5 6) writes that in Rema Yoreh dea siman 73,6 the Remah which supersedes the darkei Moshe (which was written earlier by the Remah) in date and is his conclusion on the matter, clearly concludes that the mixture does become a neveila if less than 60 times Heter, even with subsequent addition of heter without knowledge of the neveila mixture in the case of the uncashered liver attached to the bird which one cooked and mixed with other birds only realising at the end there was a problem:
בתשובת רבינו עקיבא איגר נ"ע ס"ס ס"ז שתמה על הש"ך במ"ש אולי הרב חזר בו דלכאורה לית ביה ספיקא דבודאי חזר הרב דהא לעיל סי' ע"ג ס"ו בנמצא כבד דבוק שכתב בהג"ה דנ"נ וצריך ס' נגד כל העוף. ולשון נמצא משמע דלא הרגישו שהכבד נשאר בעוף עד אח"כ שנמצא כן הרי אף בלא נודע אמרינן נ"נ וכן פסקינן סימן ע"ב ס"ג גבי לב
Everything becomes אסור, because before you added the water the meat and milk became חנ׳׳ן and in turn made the added water אסור as well (based on how the ש׳׳ך ס׳׳ק ט׳ explains the מחבר in סי׳ צ׳׳ט ס׳ ה׳). The דרכי משה argues and says that you only say חנ׳׳ן when you know the mixture occurred. In our case that you only found out that milk fell into the pot, after you added water, חנ׳׳ן never happened, so you could be מצטרף the water with the meat to be מבטל the milk.