Historically,
Way back when, circa WW II and before, there was a time they used mercury based primers and the mercury would attack the brass and form an alloy that ruined the brass for reloading. That has not been the case for 50 years or more. Before that there were corrosive primers and the salts might corrode the cases acting with water from where ever.
If you are sure of the "only 3 years old" date... I think the NRA said that brass hardens, loses its anneal over a LONG time. Like 100 years. You have a way to go. There were some rounds loaded for WW I with a plated bullet. The plating reacted with the brass and made for much increased bullet pull... and cracked case necks. And sometimes crud in the fired powder/ primer might react with humidity. (Had some PMC that got green stored in a humid atmosphere. Nothing that a light tumble would not take care of.) Yes, ammo cans are great, except for the prices. I used to pay $0.50 for 50 cals... So get to it when you can and it should be "good to go" with normal attention.