Hi, I'm surprised by the structure of this phrase, and my book contains sometimes some faults, or is it a colloquial language? The "of" looks to me unnecessary here.
https://books.google.fr/books?id=ZfiREZrremoC&lpg=PT296&ots=ZAAuV_UrFq&dq=%22if%20he'd%20of%20yielded%22&hl=fr&pg=PT296#v=onepage&q=%22if%20he'd%20of%20yielded%22&f=false
https://books.google.fr/books?id=ZfiREZrremoC&lpg=PT296&ots=ZAAuV_UrFq&dq=%22if%20he'd%20of%20yielded%22&hl=fr&pg=PT296#v=onepage&q=%22if%20he'd%20of%20yielded%22&f=false