The same analogy can be said for other fillers in the other albums. There would be one, two, or three tracks that stick out like a sore thumb, but that doesn't mean they are the leftover tracks or "rejects".
Step One has "Experienced", "Two Weak Too Resist", "Stay With Me". Steptacular has "I Think It's Love", "Moving On", "Make It Easy On Me". Buzz has "Wouldn't Hurt So Bad", "Happy Go Lucky", "Buzzz". Tears have "Firefly", "Space Between Us", "You Make Me Whole". Part 2 is far the leftover label in my opinion. I am enjoying it through and through.
I trust Steps would give their absolute best every single time and that's picking the best tracks for Part 2. If Part 2 tracks aren't good enough, I don't think they would have had the confidence to release it in the first place.