LGPE Legality question on Alola NPC Trades

[DocKlok]

When trading with the NPCs in Let's Go Pikachu and Eevee, how much of the traded Pokémon is set in stone? Can they have different natures, abilities? Looking at the legality source for trades I see this:

            new EncounterTrade { Species = 019, Level = 12, Form = 1, TrainerNames = T1, TID7 = 121106, OTGender = 1, Shiny = Shiny.Random, IVs = new[] {31,31,-1,-1,-1,-1}, IsNicknamed = false }, // Rattata @ Cerulean City, AV rand [0-5)
            new EncounterTrade { Species = 027, Level = 27, Form = 1, TrainerNames = T2, TID7 = 703019, OTGender = 0, Shiny = Shiny.Random, IVs = new[] {-1,31,31,-1,-1,-1}, IsNicknamed = false, Version = GameVersion.GP }, // Sandshrew @ Celadon City, AV rand [0-5)
            new EncounterTrade { Species = 037, Level = 27, Form = 1, TrainerNames = T2, TID7 = 703019, OTGender = 0, Shiny = Shiny.Random, IVs = new[] {-1,-1,-1,31,31,-1}, IsNicknamed = false, Version = GameVersion.GE }, // Vulpix @ Celadon City, AV rand [0-5)
            new EncounterTrade { Species = 050, Level = 25, Form = 1, TrainerNames = T3, TID7 = 520159, OTGender = 1, Shiny = Shiny.Random, IVs = new[] {-1,31,-1,31,-1,-1}, IsNicknamed = false }, // Diglett @ Lavender Town, AV rand [0-5)
            new EncounterTrade { Species = 052, Level = 44, Form = 1, TrainerNames = T4, TID7 = 000219, OTGender = 0, Shiny = Shiny.Random, IVs = new[] {31,-1,-1,31,-1,-1}, IsNicknamed = false, Version = GameVersion.GE }, // Meowth @ Cinnabar Island, AV rand [0-10)
            new EncounterTrade { Species = 088, Level = 44, Form = 1, TrainerNames = T4, TID7 = 000219, OTGender = 0, Shiny = Shiny.Random, IVs = new[] {31,31,-1,-1,-1,-1}, IsNicknamed = false, Version = GameVersion.GP }, // Grimer @ Cinnabar Island, AV rand [0-10)
            new EncounterTrade { Species = 026, Level = 30, Form = 1, TrainerNames = T5, TID7 = 940711, OTGender = 1, Shiny = Shiny.Random, IVs = new[] {-1,-1,-1,31,31,-1}, IsNicknamed = false }, // Raichu @ Saffron City, AV rand [0-10)
            new EncounterTrade { Species = 105, Level = 38, Form = 1, TrainerNames = T6, TID7 = 102595, OTGender = 0, Shiny = Shiny.Random, IVs = new[] {-1,31,31,-1,-1,-1}, IsNicknamed = false }, // Marowak @ Fuchsia City, AV rand [0-10)
            new EncounterTrade { Species = 103, Level = 46, Form = 1, TrainerNames = T7, TID7 = 060310, OTGender = 0, Shiny = Shiny.Random, IVs = new[] {-1,31,-1,-1,31,-1}, IsNicknamed = false }, // Exeggutor @ Indigo Plateau, AV rand [0-15)
            new EncounterTrade { Species = 074, Level = 16, Form = 1, TrainerNames = T8, TID7 = 551873, OTGender = 0, Shiny = Shiny.Random, IVs = new[] {31,31,-1,-1,-1,-1}, IsNicknamed = false }, // Geodude @ Vermilion City, AV rand [0-5)

It looks like 2 certain IVs are guaranteed to be perfect, the others (-1) are random, their shiny status is random, their AVs are random (within range) and that's all I see. Are gender, natures, and abilities randomized too?

[Kaphotics]

If it's not specified, then it's random.

[DocKlok]

7 minutes ago, Kaphotics said:

If it's not specified, then it's random.

Thank you. I wanted to change the nature of one of my Alola traded Pokémon but wasn't sure if that would make it illegal. Didn't know about the fortune teller NPC until later.