I am sure the the British Library has ensured everything is out of copyright, but just limiting the books to before 1899 is not enough in the UK. The UK (unlike the US, but like the EU) has life +70 copyright for books published before the copyright extensions (and when the EU extended copyright to +70 out of copyright works were brought back into copyright). For example, Shaw's works only came out of copyright in 2020. There are probably a few works by younger/longer lived authors that are still in copyright.