I suppose it all depends on how one defines "promiscuous".
No man (enjoys) being rejected period. If a man has made up his mind that he's just out to have a good time or play the field he could care less!
Odds are he has no way of (knowing) how active her sex life has been unless she tells him or he and possibly others he knows have witnessed it.
There use to be a saying if you ever talk "numbers" with men and women. Whatever he claims his number is divide it by 2 and whatever she claims her number is multiply by 2. :-)
Some guys have the mentality that if she said "yes" to them then she'll say "yes" to ANY guy. Personally I have never bought into that way of thinking. That would be like getting a new job and telling yourself; "If they hired me they'll hire anybody."
While no one wants to over inflate their head you can't have much lower self-esteem than to believe there is nothing "special" about you.
The (older one becomes) the less concerned they are about a person's past relationships. Imagine being 40 and dating someone else who is 40 and they lost their virginity at age 17 and have never been married. If they averaged (2 lovers a year) over the course of those 23 years it would mean they've been with 46 people!
Not many people over the ages of 40, 50, or 60+ are going to ask someone about the gory details/numbers. They'll just concern themselves with the kind of person they are today.
Ultimately it all comes down to the individual man. Some men have married porn stars and prostitutes/escorts.
There is someone for everyone!