Coitus interruptus, aka pulling out, aka withdrawal probably didn't happen reliably between a man and the prostitute he paid to have sex with. Think about it: it's hard enough between people in a relationship where there's mutual trust because it's so difficult for a man, when he's experiencing the ecstatic pleasure before orgasm, to rationally decide to pull out at the last minute. Now imagine him doing the same when he's about to release in the vagina of a prostitute he paid and he probably won't ever see him again, not to mention that child support laws were pretty much nonexistent back then and these women probably had sex with countless men so a man who impregnated a prostitute would have easily gotten away with it.