Therefore only 3 games are unknown...sort of...if you made the playoffs, it will be against playoff opponents from previous year.
Not accurate.
Only
2 games are not fixed and they are once last season is over.
Those 2 games are against same-place finishers in the two other NFC divisions you don't play this year.
6 NFC east games
4 AFC division games (rotates every 4 years)
4 NFC division games (rotates every 3 years)
2 NFC games against same-place finishers (1st place vs 1st place, 4th vs 4th)
For example, we already know the Cowboys will play at the Rams in 2020 (I'm going) and I've always wanted to go see a Chiefs game, so I will travel to Kansas City in 2021 when the Cowboys travel there.
The reason the schedule announce is such a big deal is because fans want to attend certain games, take trips,
AND
fans, media, advertisers, etc., want to see when the marquee match-up's will occur.