In August 2020, Polkadot was redenominated, which influenced the amount of existing DOTs. With that, currently, there is the amount of 1 billion DOT tokens.
This redenomination happened to avoid the use of small decimal places, thus facilitating the calculation of the entire system. In other words, for every 1 DOT a person had, he now has 100.
At the time of the change of name, Polkadot itself made a publication explaining that this movement would not impact the economy of the ecosystem, which is very relevant information for users of the network.