Since it was Bitcoin, then BCH/BCL and now BTCC, the blockchain was always publicly mined by a multitude of people.
- If you had BTC on block #478558 and haven't spent them before later forks, your coins are present on BTCC.
- If you had BCH on block #504031 and haven't spent them before later forks, your coins are present on BTCC.
- If you had BCL/BCHC on block #576697, your coins are present on BTCC.
No changes were done on the coin supply or distribution. BTCC had and follows the normal mining of a blockchain, no airdrops etc.
What does it mean "haven't spent them
before later forks"? As long as one has the private key at those specific blocks, it shouldn't matter if the coins were spent later, unless the private key became compromised?