A change in the Pokedex that is related to Pokemon Gyms can now be seen. How the Pokemon sightings in the Pokedex will be recorded was already altered. Pokemon which can be seen in gyms will be automatically considered as sightings in the Pokedex. Thus, it will be added as a silhouette of a Pokemon and as an addition to the single listing into the Pokedex. It can be noted previously that only wild Pokemons, which can be seen in the wild, were the only ones which will qualify as sighting in the Pokedex.
According to Game Rant, there were various responses to this change. Some of the players were happy with the update, while others find this disappointing. There were some of the Pokemon Go fans who are concerned about the ratio of their caught to sightings. Because of this change, the ratio could have the possibility to be undone by simply seeing specific Pokemon in Gyms. These Pokemons might not even be caught. Despite of all the series of opinions related to these change, there were players of the core Pokemon series who quickly emphasized that the Pokedex has always been recording sighting of new Pokemon in Gyms and trainer battles in its original games. It can therefore be concluded that there is significance for Niantic to place this change into the mobile game of the Pokemon series.
This change is nothing major, and it did not heavily change the process on how the game was played - there will be more updates which will come for the game. Niantic has already made known about an update that will allow members of the same team to easily participate in terms of strengthening their team's Pokemon Gym. In this manner, it will be more convenient for trainers to catch rare Pokemon that is if they already have enough amount of more common Pokemon that have the same type. On the contrary, the trainer battles and the Pokemon Go trading's expected release window is not yet announced.
Meanwhile, check this video below on how gym battles work.