אתם נצבים – Rashi says that this gathering took place on the day of Moshe’s eventual death. The Sifsei Chachamim explains that Rashi learned this from the word היום as a reference to the known day of which Moshe later says בן מאה ועשרים שנה אנכי היום .
However, perhaps as a bit of a drush of מילתא דבדיחותא we may ask that Rashi make no mention of the word היום and in most prints, it is not even in Rashi’s dibbur hamaschil!
Perhaps we can say with a bit of humor, that we know the parsha always hints to the time of year. Rashi knew it was the day of Moshe’s departure simply because אתם נצבים – they were all STANDING! - Why were they all standing at this meeting? They must have not had a seating gabbai!
Why not? Wasn’t Yehoshua always the one to set up the seating in the Ohel Moed? Why did he not do so that day? It must be that it was the day of Moshe’s departure and subsequently Yehoshua’s day of malchus. It would be inappropriate for Yehoshua to be serving as Mishares Moshe and the seating gabbai on the same day of his inauguration.
Hence, they were all left standing. 😉