Could of, would of, should of are probably because teachers /parents say would've, could've, should've rather than the whole words. could have, should have, would have. listening to it it could easily be mistaken for would of etc
I'm dyslexic but try really hard to work out everything before posting, it's not easy for me especially when I make a mistake and just cannot see it. I was put into the dunce class at school (back in the 60s) and it affected me a lot confidence-wise. I am not that bad now but really hate it when you are debating a subject someone pulls you up on spelling or grammar. Time and a place
I remember a lovely man on a digital spy who made a thread especially for me and others like me where people who were good at these things could explain how and why we were going wrong in a sentence we had posted on other threads. it was non-judgmental and really helpful
Sorry went off on one a bit there.