Missing Megastones from Battle Arena

Is it possible to create a system where an NPC sells you Megastones, but only the ones you have already discovered for those that lost items to the Battle Arena before the next update? I was experimenting with different teams and ended up losing a few Megastones that are only one time obtainable (Delta Gardevoirite and Delta Scizorite) as well as a Crystal Piece, but I still have 2 left so that is not as big of a deal. Is there any way besides transferring from another save to get them back? Thank you

It’s possible to revert to a backup save to a save before the megastones went missing.

How far back do the saves go? I think I lost them a week ago. Ugh I feel so stupid for not noticing sooner.

There are 3 backups. One goes to the save directly before the current one, the second corresponds to the save before that, and the third is the one before that. They’re not based on time, but rather the last 3 in game save points.

If I lost them before 3 saves ago, then they are gone? If I can’t get them back, it’s fine bc I can always transfer. Thanks for the information!