Private bills have existed for for quite a while. You have to understand that most places that inherited common law also inherited ‘parliament’s sovereignty’,

Private bills have existed for for quite a while. You have to understand that most places that inherited common law also inherited ‘parliament’s sovereignty’, the legal notion that no bill or law can constrain the power of parliament. Now that has been curtailed in quite a few places but the notion still fully exists (I believe it was used recently by the UK Supreme Court to force the government to give parliament a vote). Australia is such a place. Even the US system had it to a degree. Originally the bill of rights only applied to the federal government, later Supreme Court rulings extended it to state law.