The way I see it is that DES exposure is a type of intersex condition, because you started off developing as male, but then the DES began to be administered, and it caused you to develop as female instead of male for the remainder of the pregnancy. It's just that with DES (and, I suspect, with the treatments that replaced it), the exposure tends to not start until too late to have much effect on genital development and the brain is the main thing that tends to be affected, so there's often not much physical indication at birth that anything untoward happened. The medical definition of intersex revolves around genitals, and it's something that usually gets diagnosed at birth. Nonetheless, they've got the same underlying cause - a disruption to that person's hormones during part of their prenatal development.
With classically defined intersex, the main focus is usually on the genitals (and often the disastrous consequences of botched attempts to "normalise" the sex of the baby). With DES (and indeed transsexuality from any cause), the main issue is psychological problems, caused by years and decades of being forced to adopt a completely different social role from the one your brain is wired up to perform, and also I think by having a body that's producing the wrong mix of hormones for your brain. So there's two completely different sets of priorities there, however there's at least one thing that DES and classically defined intersex have in common - you're at high risk of experiencing problems with fertility, and of developing health problems as you get older due to your testosterone production falling below the minimum needed to maintain good health (if you transition then that's no longer an issue, because the estradiol you take as part of your HRT performs the same functions as far as your body's concerned as testosterone, except the female version of them).
DES lost it's FDA approval in 1971, however doctors in the US continued to prescribe it off label for several years after that, and I've chatted to DES daughters who were born in the mid-70s in the US. Elsewhere, it continued to be used throughout the 1970s (and right up until 1983 in Spain I think).