I cooked a vegetable dish for a sheva brachos and then cooked meat in the same pot, assuming that it was fleishig.
After cooking a significant amount of meat, I realized that the pot was really milchigs and had been used earlier in the day to cook milchige oatmeal. Throwing away the meat would be a significant financial loss, and would put great pressure on me for tonight’s sheva brachos. Can I use the meat?
If I can use it, I have a second question. There will be many distinguished roshei yeshiva at the sheva brachos. Do I need to tell the roshei yeshiva that a shailah was asked regarding the meat?
In regards to your first shailah, the Rashba (Toras Habayis 4,4,37b) rules that if vegetables or any other pareve food was cooked before the meat, the taste of the milk in the pot is weakened, and the food is not considered bosor becholov.
According to this understanding, the meat in question would be kosher.
However, the Bais Yosef (93:1) explains that many Rishonim disagree with the Rashba and rule that since the meat was cooked in a milchige ben yomo pot, even if vegetables were cooked in between, the meat is bosor becholov.
According to this understanding, the meat in question would be forbidden.
Although the Shulchan Aruch (Yoreh Deah 93:1) and most poskim argue with the Rashba, the Shach (Nekudas Hakesef, Yoreh Deah 93:2) defends the Rashba’s understanding and explains that this is the opinion of most Rishonim.
In a case like yours, where there is great need (i.e., financial loss and preparation for the simcha), you may rely on the Shach’s ruling and use the meat.
As far as your second shailah about telling the roshei yeshiva, not only do you not have to tell them, but it is actually forbidden to reveal this information.
Once it has been halachically decided that the meat may be used, it is 100% kosher. The knowledge of this shailah will spoil the simcha of the chosson and kallah, which is a significant transgression.