Anyone using PGE2 will be using it exogenously so very unlikely to get that. Also balding scalps have significantly less PGE2 in them to start with so it would take an awful lot to cause this I think. People are using literally minute doses of this.
Sulfa is a proven drug with safety trials, correct me if I'm wrong but although Sulfa is a drug with a lot of side effects I don't think Nail clubbing is one of them and if it is, it's for people on very high dosages a day I would bet, (3 grams+) most people using it for male pattern baldness are not on more than a gram if that.
With regards to Castor oil, taking <5ml per day is not dangerous at all lol, it is actually good for you and can help your skin as well as numerous other health benefits. If you're taking more than 5ml a day? Well I think you will have more immediate problems than the potential for nail clubbing.