Any type of oral sex is considered NO RISK.To answer your question about someone being infected for years and never seroconverting,that,s never been substantiated.Cases of latent seroconversion at 6months or more occured in the 1990,s.
Transmission happens when having unprotected vaginal/anal sex penetrating the tissue inside the vagina/anus...
Sharing needle for drug use...
Mother to Child...
Exposure happens inside the body, not outside!
It is a myth that seroconversion can happen years later, people have said that from the start, is that really possible, no. HIV does not hide for antibodies