Challenger Series was included in the last Worlds criteria. It's part of Tier 3.

for my lack of reading comprehension.
I think a strong argument can be made for taking the skaters who have caught lightning in a bottle. Upsets don't happen that often at nationals, and when they do, and when those skaters have been chosen for the big assignments, they have tended to compete well at those worlds/Olympics: e.g., Galindo in '96, Evora/Ladwig in '10, Nagasu in '10, Brown in '14, Edmunds in '14. There's something to be said for taking who is hot.
Galindo had been repeatedly lowballed by USFS and eligible US champions were guaranteed spots for Worlds. While because of TV money they couldn't officially grant US champions the spot, they did, even if they also gave an injury bye. That kind of "lightening in a bottle" was beyond USFS control to shove back in, and there was no body of work concept, even if it wasn't called that except to determine a medical bye. Especially since 1996 was still part of the skating boom, and people were watching US Nationals like a hawk, and he had the best fluff.
Body of work cuts both ways: if a skater/team has good opportunities and the international judges and callers are making it clear how they score a skater, then giving a skater who excels at Nationals and has a junior resume -- which both Edmonds* (JGPF, 4th, <2 points behind Medvedeva) and Brown (respectable in his first senior GP, medalled in his second, after USFS tried to force him to stay junior another year, and they still didn't send him to Worlds) -- did isn't that exceptional, unless the skater left home has major endorsements.
"Lightening in a bottle" at US Nats often doesn't translate into a second peak a month or even 2-2.5 months later, even for seasoned competitors, and USFS often gives love to skaters at Nationals that international judges don't. Evora/Ladwig were an exception by scoring over 170 internationally at the Olympics, which was within 2 points of the Nationals scores, also 20-30 points over their GP scores (in the 140's), whereas it usually translates into an ~ 20 point drop, like for Ryan Bradley between 1st at US Nationals and 13th at Worlds.
It's not simply placements: results can include the strength of the field, the scores -- is the difference between podium and 6th 4 points? 15 points? a start order of 10/37 vs. 34/37? -- the protocols, the strength of the competition, was a skater suffering from food poisoning, and all of that has to translate into whether it's worth setting aside US Nats results, at the top of the list for 2013 and the top of Tier 3 for 2018. And, they get to make up from skater to skater what criteria they are using.
*I don't think USFS, in the first year of using this to their perceived advantage, was willing to override US Nats results for two spots. (I think they would have dropped Edmonds, if her and Nagasu's scores had been flipped, even if Nagasu was coach-less.) And until the US #1 Pair is in a position for US to earn three Pairs spots, I don't think they care which US#2 they send. I hope that the Knierims don't make USFS have to make a tough decision in Pairs with China in pursuit for the team bronze.
If you look at other results besides placement, then, so far, adding in the early CS events to Tier 3:
Chen:
Tier 1:
3. 2017 Worlds: 4th-199.29
Tier 2:
2. 2017 4C's: 12th-166.82
Tier 3:
1. Challenger Series:
- USIFSC: 3rd -182.32
2. 2017 US Nats: 1st-214.22
Wagner:
Tier 1:
3. 2017 Worlds: 7th-193.54
Tier 2:
2. 2017 4C's: N/A
Tier 3:
1. Challenger Series: N/A
2: 2017 US Nats: 2nd-211.78
Nagasu:
Tier 1:
3. 2017 Worlds: N/A
Tier 2:
2. 2017 4C's: 3rd-194.95
Tier 3:
1. Challenger Series:
- USIFSC: 2nd-183.54
2: 2017 US Nats: 4th-194.90
Bell:
Tier 1:
2. 2017 Worlds: 12th--187.23
Tier 2:
2. 2017 4C's: 6th-177.10
Tier 3:
1. Challenger Series
- USIFSC: 6th-168.66
2. 2017 US Nats: 3rd-197.92
Zhang:
Tier 1:
2. 2017 Worlds: N/A
Tier 2:
2. 2017 4C's: N/A
Tier 3:
1. Challenger Series:
- Ondrej Nepela: 6th -- 167.95
2. 2017 US Nats: 5th
Tenell:
Tier 1:
2. 2017 Worlds: N/A
Tier 2:
1. Challenger Series:
- Lombardia: 4th-196.70
2. 2017 US Nats: 9th-169.98
Tier 3:
3. 2017 Jr. Worlds: 7th-161.36
4. 2017 JGPF: N/A
Andrews:
Tier 1:
2. 2017 Worlds: N/A
Tier 2:
2. 4C's: N/A
Tier 3:
1. Challenger Series: N/A
2. 2017 Nationals: N/A -- I don't remember Jr. Nationals counting, but if they are, 2nd-155.14
3. 2017 Jr. Worlds: 12th-149.05
4. 2017 JGPF: N/A