Wow. That is an awesome resource.
It's good, but it's a little light on details. For example, the Lakers can't trade an unprotected first until 2021, yes. But for that to occur, it means:
1) They had a top 5 pick in 2015, so didn't give their pick to Phoenix
2) Had a top 3 pick in 2016 so didn't give it to Phoenix
3) gave their pick to Phoenix in 2017
OR
1) Gave their pick to Phoenix in 2015 or 2016, and then
2) Had a top 5 pick in 2017 (if they gave their 2015 pick to Phoenix, otherwise it doesn't matter)
3) Had a top 5 pick in 2018
That's a lot of top 5 picks in there. Assuming they do not have a top 5 pick in 2015 (more likely than not) and in 2017, they will be able to trade an unprotected 2019 1st rounder.