Double and triple sessions of making love used to occur regularly (when I was younger) with both my wives. I've never bothered with using a condom since having a vasectomy at age 34. so "sloppy seconds" have been a familiar experience for me -- though only in my _own_ cum.
The feeling of making love in one's own cum is delightful, and my love partners have always enjoyed it too!
The most memorable multi-orgasmic experiences I've had were during my four-month affair (during my first marriage) with a 34-year-old woman when I was 55. Whenever she and I could get together for at least eight hours, we would make love repeatedly, up to 4 times typically, and up to 5 or 6 times if we could spend at least twelve hours together. I recall that once, when we got together briefly three days after one of those 6-session occasions, she complained that her vagina was still sore; but though that particular meeting had to be short, I quickly succeeded in soothing her soreness by licking and sucking her clitoris till she was lubricating profusely, and we proceeded to a mutually satisfying session of penis-in-vagina love-making.
I remember especially one time when my mistress and I were able to spend the night together. We made love; I fell asleep with my penis still hard in her vagina, and woke up about an hour later still hard in her. She told me proudly that she had kept me hard in her by squeezing my penis frequently (thanks to her regular kegel exercises, she had amazing control of her vagina, and could actually milk me to an orgasm just with her vaginal muscles). We immediately made love again, and then repeated our love-making twice more that night; sleep was just a brief diversion.
Ah, how I wish I could be only 66 again! That's when I achieved my largest number of orgasms in one day (more exactly, the largest number that I recorded at the time -- I have no doubt that I exceeded that number when I was in my teens and 20s, and probably even in my 30s, especially after my vasectomy). That day at age 66, I had 8 orgasms in 11 hours, with all but the penultimate one being ejaculatory orgasms. (The last few of them were solo, rather than with my wife -- she'd gotten too sore from the first several times to want to continue.)
Sadly, I've slowed down in the 16 years since then, but <sigh> that appears to be an inevitable accompaniment of aging. At least I can attest that still, at age 82, practically all of my orgasms continue to be ejaculatory, though these days I just dribble.<sigh>