Airdrops were made to those who purchased Booster Packs from the official shop. This is common for most of the sales conducted by @splinterlands over these 5 years. Additionally SPS was Airdropped based on Collection Power + Nightmare Packs + Land. I think there was Title owners were also rewarded. Follow the following links to see if you are eligible for any.
https://splinterlands.com/?p=rift_drops
https://splinterlands.com/?p=cl-airdrops
Some Airdrops were discontinued. I don't remember what happened to the unclaimed assets. It's best to ask on Discord.