Is Bitcoin increasing their Bitcoin Private Key characters?

[Honey9]

I have some bitcoin private keys of 51 characters.
I've a question that why bitaddress.org generating 52 characters bitcoin private keys?
How many characters were on 2011 of Bitcoin Private Key?
Is Bitcoin increasing their Bitcoin Private Key characters?
Thanks.

[OmegaStarScream]

For private keys associated with uncompressed public keys, they are 51 characters and always start with the number 5 on mainnet (9 on testnet). Private keys associated with compressed public keys are 52 characters and start with a capital L or K on mainnet (c on testnet).

See here for more details: https://en.bitcoin.it/wiki/Private_key