I'm thinking S3 might need to move to 2022. While in the first episode, there are numerous references to it being a year. Whether it's Summer 2021 or 2022 requires some leniency in what qualifies as a year. S2 does have Dawn of the 7 releasing in Summer 2021. However, due to Stormfront, there were reshoots, so it getting delayed a year makes sense. Gen V also apparently has the 2022 calendar and the Seven on Seven videos cover in-universe until January 2022. All the references to it being a year are what complicate things. S2 confirms a Fall 2020 setting through stuff like the September 30th date on the obituary, 2020 on the same obituary as well as the year given for Translucent's death, and the weather. However, the Seven on Seven videos cover July 2021-January 2022 and with Homelander's birthday being July 4th, S3 has to begin in June 2022.
As for most of the other YouTube videos, I'm just placing them when they were uploaded since that's the case for the Seven on Seven videos. With exceptions for stuff like the Soldier Boy PSA from 1984.