here is some info - but not what I am looking for... I'm determined and WILL find it - this merely mentions it:
"Ten per cent of the women studied released two eggs in the same month. And all the women examined by researchers at the University of Saskatchewan in Saskatoon, Canada showed at least two waves of maturing eggs in their ovaries in the same month"
On a personal note, this happened to ME recently, which is why I researched it and found this out. I took very long to ovulate, and my monitor was showing NO estrogen or LH surges day after day. But, I could tell from other signs (EWCM, libido, cramps, moods, acne, ie signs of surging estrogen) that I WAS building toward ovulation - and my fertility acupuncturist confirmed this from my pulses.
Finally, one day I went to her and said I think I just need help popping this out, which she confirmed from my pulses, she put in the needles and immediately my right ovary started pinging away, like rapid fire fluttery cramps. She read my pulse and said yep you just ovulated. When i got home, a couple hours later, I got my teltale, never-fail sign of ovulation which is a thin bright red streak/line of blood in my cervical mucus.
Next day I woke up and was v confused b/c now suddenly I felt an impending OV on the LEFT side. I called up my acupuncturist and she said, it's a v small chance but come in just in case, and sure enough, my pulses showed I had another egg waiting to release on the opposite side. She did her needles, and immediately PING my left ovary started firing; two hours later - yep, red streak. Double ovulation! ALthough, since theywere almost within 24 hours of eachother, that might be considered "single ovulation, two eggs".
If I had conceived on that cycle (we didn't) it would have been twins who were a day apart in gestational age (assuming they had implanted at same time). And if I'd been messing around on my hubby, I could have been one of those news stories you hear about where a woman has twins from two different fathers!

PS - My fertility doctor insisted it's highly unlikely but I just knew it had happened to me so I researched it online and got the above study, and also the following:
https://pregnancy.lovetoknow.com/wiki/Can_You_Ovulate_Twice_in_One_Cycle
...It used to be that twins were either fraternal or identical. However, with more advances in genetic testing, scientists are learning that there are perhaps more possibilities for twinning (and, therefore, ovulating twice in one cycle) than meets the eye.
Fraternal Twins of Different Gestational Ages?
In general, fraternal twins are the result of two eggs released within the same 24 hour period and then fertilized by two different sperm. However, in superfetation, a mother releases one egg, gets pregnant, and then releases another egg in a different cycle--her cycle not stopping during pregnancy the beginning of pregnancy. If both eggs are fertilized, this results in twins that have different gestational ages. It has been reported to have occurred, but is extremely rare.