My guess is that it takes a lot of energy for veemon to armor digiviolve into him. Maybe it dissapeared. But I also thought he would because kari said "only a miracle" can help so I thought digiegg of mircles. Also malomyotismon stopped it from happening.
Episode 21 of Digimon Adventure.
Episode 37 of Digimon Savers.
episode 35 near the end
Her first chonological appearence is in the first Digimon movie. If you are referring to her first appearence in a proper Digimon season it happened in the 21st episode of Adventure.
All of them evolve into their Rookie forms in the first episode. Agumon becomes Greymon for the first time in the second episode. Gabumon digivolves into Garurumon in the third episode. Biyomon becomes Birdramon in the fourth. Tentomon becomes Kabuterimon in the fifth. Palmon becomes Togemon in the sixth. Gomamon becomes Ikkakumon in the seventh. Patamon becomes Angemon, dies and becomes an egg in the 13rd episode. Poyomon's egg hatches in the 14th episode. Poyomon regains the power to digivolve into Tokomon in the 15th episode. Agumon gets corrupted into SkullGreymon in the 16th episode. MetalGreymon debuts for the first time in the 20th episode. Tokomon regains the power to digivolve into Patamon in the 22nd episode. WereGarurumon debuts for the first time in the 23rd episode. MegaKabuterimon debuts in the 24th episode Garudamon debuts in the 26th episode. Patamon regains the power to digivolve into Angemon in the 33rd episode. Lillymon debuts in the 35th episode. Zudomon debuts in the 36th episode. Gatomon joins the group and digivolves into Angewomon in the 37th episode. Agumon and Gabumon warp digivolve into WarGreymon and MetalGarurumon in the 38th episode. MagnaAngemon debuts in the 52nd episode.
Episode 33 of Digimon Tamers.
The next season after Digimon Tamers is called "Digimon Frontier".
The first episode of the Digimon Xros Wars, which is the next season.
Episode 51 of Digimon Adventure.
Episode 38 of Digimon Adventure.
Episode 15.
Digimon Adventure 02 Episode 38: A Very Digi-Christmas