^^^ At least
@AngieNikodinovLove finally noticed my mention of AN from last week.
@Frida80, I believe these are the relevant excerpts from the
2017/18 ISU JGP Announcement document (I've bolded the key parts below):
2.1 Men and Ladies
...
Additional Entries For Men and Ladies, if any ISU Member mentioned under a) to c) does not use its right to enter Skaters in the competition concerned, this entry will be given to the first ISU Member, mentioned under b) for an additional entry.
...
2.4 Procedure of Nominating and Deadline
The following procedure is necessary to control and to calculate points as well as to offer possible changes of non-used slots within the various events: a) Entries by number ISU Members must announce by June 15, 2017 at the latest, to the ISU Secretariat, their participants by number for all seven events of the ISU Junior Grand Prix of Figure Skating. The official forms must to be used. The ISU Members must also announce by June 15, 2017 the disciplines and/or the events in which they were originally entitled to enter participants but will not use this right.
...
Based on the information received from the ISU Members, the ISU has informed the ISU Members concerned about changes or additional possibilities to enter Competitors, after June 15, 2017.
Bottom line, as I see it: Countries do not have to give up their earned JGP spots to any other country -- they can file the official paperwork by the June 15th deadline that confirms they plan to keep all their earned spots even if they don't intend to use them all or end up not using them all for whatever reason.
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14 age-eligible U.S. ladies currently have both minimum scores (20 / 35) for 2018 Junior Worlds and 12 are currently listed in USFS' International Selection Pool:
Starr ANDREWS USA Golden Bear 2016 27.10.2016 37.27 J / 54.61 J
Ting CUI USA Philadelphia Summer International 2017 03.08.2017 31.73 J / 52.98 J
Hanna HARRELL USA Asian Open FS Trophy 2017 02.08.2017 32.40 J / 47.83 J
Tessa HONG USA ISU JGP Tallinn Cup 2016 29.09.2016 31.42 J / 39.54 J (assigned to JGP #4 in Minsk)
Angelina HUANG USA ISU JGP Cup of Austria 2017 01.09.2017 21.77 J / 48.03 J
Ashley KIM USA Golden Bear 2016 27.10.2016 26.41 J / 37.11 J
Ashley LIN USA ISU JGP Ljubljana Cup 2016 22.09.2016 31.80 J / 47.86 J (assigned to JGP #3 in Riga)
Emmy MA USA Challenge Cup 2017 23.02.2017 28.63 J / 46.41 J (assigned to JGP #3 in Riga)
Brynne MCISAAC USA ISU JGP Cup of Mordovia 2016 16.09.2016 25.32 J / 38.84 J (currently not listed in this season's ISP)
Kaitlyn NGUYEN USA ISU JGP Brisbane 2017 24.08.2017 32.04 J / 57.78 J
Gabrielle NOULLET USA ISU JGP Yokohama 2016 09.09.2016 27.75 J / 35.44 J (currently not listed in this season's ISP; returning from injury)
Nina OUELLETTE USA ISU JGP Pokal d. Blauen Schwerter 2016 06.10.2016 25.90 J / 50.48 J
Paige RYDBERG USA Philadelphia Summer International 2017 03.08.2017 21.80 J / 49.65 J
Megan WESSENBERG USA ISU JGP Czech Skate 2016 01.09.2016 31.53 J / 45.19 J
Has the SP minimum only:
Audrey SHIN USA Asian Open FS Trophy 2017 02.08.2017 23.42 J / 34.61 J (came up 0.39 short in Hong Kong)
Has aged out of ISU Junior:
Bradie TENNELL USA ISU World Junior Championships 2017 17.03.2017 32.53 J / 52.81 J
ETA - ISU Junior age-eligible ladies currently listed in USFS' ISP and JGP alternate lists who have not been assigned an international to date: Ashley Kim, Vivian Le, Akari Nakahara, Nina Ouellette, Jenna Shi.