Maso05

Additionally, you can also obtain Groudon's seen data from battling Nikola boss in Unknown Place, located in Trainer's Valley. Source: Maxie (boss), PROwiki If you have battled both of the mentioned bosses above and or Nikola before, and somehow it hasn't registered Groudon's seen data, there is a PC in Prof Oak's Lab in Pallet town that may restore seen data of Legendaries. I had to recently use it to restore one of the trio beast's seen data. Not sure if this will be of any use for you regarding this case. But worth a try, worst case; it won't work for you. Source: Professor Oak's Lab, Pallet Town, PROwiki