Why are there 8,300 Apes on Opensea and not 10,000?

Ape Gang was initially launched using an Opensea based ERC 1155 NFT contract.
A new ERC-721 contract (the gold standard) was created in December 2021.
The process of moving Apes from the old contract to the new contract is done manually by each holder. This migration is still ongoing which is the reason why only 8,300 are visible on Opensea. 8,300 is the number of Apes that have migrated to the new contract.
The old ERC 1155 contract Apes cannot be bought or sold any more. Owners of these Apes must migrate to the new contract to be able to trade their NFT. Because of this, we expect a steady rate of Apes to migrate to the new contract over time. Ape Gang predicts we will hit around 9,000-9,500 Apes at maximum due to lost wallets.